Kamala Harris will tonight face the biggest test of her political life so far when she addresses the Democratic national convention in Chicago in a bid to persuade American voters to defeat Donald Trump in November’s presidential election and put her in the White House.

The vice-president’s rocket-fueled campaign is still barely a month old following Joe Biden’s decision to withdraw from seeking re-election in the face of a disastrous debate performance and questions over his age and mental acuity.

Harris, and her vice-presidential pick Minnesota governor Tim Walz, have quickly overturned the election’s narrative, turning a solid Trump lead in the polls over Biden into a slight – but clear – advantage over the former Republican president.

In addressing the Democratic convention on Thursday night – and by proxy the wider US electorate watching in their millions on television – Harris will be making a direct pitch to voters to back her vision for the United States.

Harris’s campaign has sought to portray a more optimistic, future-focused view of the country than her rival, and perhaps also than that of the president, who based much of his pitch on dark warnings of Trump’s autocratic sympathies.

Over the course of the week at the convention, the audience has heard from the Democratic party’s most powerful players, who threw their support unequivocally behind Harris. Biden, Barack and Michelle Obama, Hillary and Bill Clinton, and Nancy Pelosi all gave primetime speeches, as did some of the party’s rising stars, such as Alexandria Ocasio-Cortez.

Now it is expected that Harris’s speech will seek to lay out her personal story as she bids to become a historic president: the first woman president and the first woman of color due to her south Asian and Black background. Her speech is likely to focus on her work as a prosecutor, defending victims of crime.

But her speech will also lay out a sharp contrast between her positive view of the country’s future prospects and Trump’s almost wholly grim warnings about the state of the nation and his focus on immigration and crime.

Across three days so far, speaker after speaker has already hailed Harris as a change-agent who would not only defeat Trump but lift the country higher, ushering in a new chapter of possibility and seek to return US politics to some semblance of normality since Trump came onto the political stage eight years ago.

The Harris campaign – and especially the outspoken Walz – has also displayed sharp elbows and an ability to insult and poke fun at Trump.

The switch in the polls and newfound edge has impressed many observers. “She has had a very good month not just because of a honeymoon, but because of the way she’s presented herself, the way her campaign has positioned her,” David Axelrod, a former top aide to Barack Obama, told the Guardian.

Certainly it seems to have unsettled Trump and his campaign. Trump has adopted a policy of directly insulting Harris and inventing a series of nicknames for her while trying to paint her as a leftwing extremist and questioning her racial identity. But the jibes have had little effect and even drawn criticism from some senior Republicans.

They have not blunted her lead. Harris consistently tops Trump by three or four points in recent head-to-head surveys and has also improved her standing in the handful of key states that are crucial to victory. While the electoral contest remains impossibly close, she has widened the battleground once more from the Rust belt states of Michigan, Wisconsin and Pennsylvania to once again include Sun belt states like North Carolina, Arizona and Georgia.

Throughout the convention so far, Democratic speakers have tried to make Trump seem small and diminished. They have sought to keep him on the backfoot and in a reactive mode, responding to attacks and being kept off-balance.

The House minority leader, Hakeem Jeffries, compared Trump to an “old boyfriend” who has spent the last four years spinning the block, trying to get back into a relationship with the American people.

“Bro, we broke up with you for a reason,” Jeffries said.

“Kamala Harris has always understood the assignment,” said Laphonza Butler, a California senator and friend of Harris’s.

“Kamala, your mom would be so proud of you,” said Doris Baptiste, a family friend who was close to Harris’s mother.

On Wednesday night, Walz offered a full-throated attack on Trump, a defense of his record running Minnesota and a passionate advocacy for Harris. After criticizing the Trump campaign, he led the crowd of cheering delegates in a chant of: “We’re not going back! We’re not going back!”

Turning to the theme of freedom – which was the focus of the night’s convention programming – Walz said: “That’s what this is all about, the responsibility we have to our kids, to each other and to the future that we’re building together, in which everyone is free to build the kind of life they want. But not everyone has that same sense of responsibility. Some folks just don’t understand what it takes to be a good neighbor. Take Donald Trump and JD Vance.”

Walz said Trump and his running mate had an agenda to only benefit the “richest and most extreme” people in the US. Walz added: “It’s an agenda nobody asked for. It’s an agenda that does nothing for our neighbors in need. Is it weird? Absolutely, absolutely. But it’s also wrong. And it’s dangerous.”

Tim Walz’s 17-year-old son Gus stole the show with an emotional display of family fealty as his father delivered his acceptance speech at the Democratic national convention in Chicago.

After the elder Walz described the painful process of starting a family using fertility treatment, television cameras focused on Gus as he stood up, with tears pouring down his face, and pointed to the stage mouthing: “That’s my dad.”

The moment overshadowed other parts of a widely-praised 17-minute speech from the Democratic vice-presidential nominee and captured the attention of watching TV commentators and social media.

“Tim Walz was 100 percent pitch perfect, grand slam, touchdown in every possible way. And yet somehow Gus Walz was even better,” posted Kate Bedingfield, former White House communications director.

“I love Gus Walz,” Jen Psaki, a former White House press secretary said on MSNBC. “I’m going to start ugly crying just talking about him.”

On CNN, Dana Bash said: “That is the clip-and-save moment that everyone is going to be seeing. If you didn’t get moved by that moment, I don’t even know. What a remarkable moment just in American life.”

The emotional scenes also captured the attention of conservative Fox News, where hosts Martha MacCallum and Dana Perino talked about how moving it was.

Even before what has now become a seminal moment, Gus seemed in tune with the symbolism and political impact of his father’s words.

“It took Gwen and I years to conceive, but we had access to fertility treatments and when our daughter was born, we named her Hope,” Walz told the gathering. At that point, Gus, already in tears, pointed meaningfully to his 23-year-old sister sitting beside him.

He stood up, put his hand over his heart and mouthed “that’s my dad” when Walz delivered his next line: “Hope, Gus and Gwen, you are my entire world and I love you.”

After the speech, Gus, climbed on the stage with his mother and sister and hugged his father, burying his face in his shoulder.

Tim Walz and his wife, Gwen, both former teachers, recently disclosed that their son Gus has a non-verbal learning disorder and attention deficit hyperactivity disorder, as well as an anxiety disorder.

In a recent statement to People magazine, the couple described how they noticed Gus’s condition at an early age but never considered it an obstacle.

“Like so many American families, it took us time to figure out how to make sure we did everything we could to make sure Gus would be set up for success as he was growing up,” they said.

“It took time, but what became so immediately clear to us was that Gus’ condition is not a setback – it’s his secret power.”

When the cameras panned over from Oprah Winfrey calling out “childless cat ladies” at the Democratic national convention, they landed on an unsuspecting woman who nodded along to Winfrey’s words and prompted plenty of reactions online – and a response from the woman herself.

During Winfrey’s speech on Wednesday, the cameras awkwardly cut to the audience member Teresa Woorman, a delegate from district 16 in Maryland.

Woorman took her moment in the limelight in stride, writing on X: “Damn right this childless cat lady is 100% disgusted by JD Vance in general and 100% behind @KamalaHarris and @GovTimWalz! Also I may be childless but I do hope that’s not a permanent condition, thanks!

“Also – funny enough I recently got appointed to a legislative seat” she added. “And I got sworn in to the Maryland House of Delegates last week and I referred to myself as a childless cat lady during my remarks. But I’m in good company, @taylorswift13 @Oprah.”

As mentioned in Woorman’s missives, Winfrey’s “cat lady” comment was in reference to earlier comments made by Vance, the Republican vice-presidential nominee and an Ohio senator.

Vance has received backlash in recent days after a resurfaced clip from 2021 emerged in which he is seen saying that the US is run by “a bunch of childless cat ladies who are miserable at their own lives and the choices that they’ve made and so they want to make the rest of the country miserable”.

During the speech on Wednesday night, Winfrey took a swipe at Vance’s comments, and said: “When a house is on fire, we don’t ask whose house it is,” adding that “if the place happens to belong to a childless cat lady, well, we try to get that cat out too”.

The cut to Woorman has since been celebrated and joked about by watchers and commenters online.

“That poor woman who the camera panned to and stayed on for seconds too long when Oprah mentioned ‘childless cat ladies’ … gurl I see you and I am so sorry but I cackled,” one X user said.

“Shady cameraman!” another person said.

“They didn’t have to do this I need an interview with her,” a third person said.

Woorman did not immediately respond to the Guardian’s request for comment.

Israel launched strikes on more than 10 areas across southern Lebanon, a spokesperson for the army said, hours after Hezbollah launched more than 50 rockets and a swarm of drones, hitting homes in the Israeli-annexed Golan Heights and wounding one person.

Israeli warplanes struck weapons depots, military buildings and a launcher used by Hezbollah in an overnight operation, Israel Defense Forces (IDF) spokesperson Daniel Hagari said on Thursday.

Hezbollah said its attack on Wednesday was in response to an Israeli strike deep into Lebanon on Tuesday night that killed one person and injured 19.

Israel’s response to the Lebanese militant group came hours after US president Joe Biden used a phone call to press Israeli prime minister Benjamin Netanyahu on the urgency of sealing a deal for a truce in Gaza and the release of hostages, according to a White House report.

The call between the leaders, in which Vice-President Kamala Harris also took part, saw Biden stress to Netanyahu “the urgency of bringing the ceasefire and hostage release deal to closure and discussed upcoming talks in Cairo to remove any remaining obstacles,” a White House statement said.

The US secretary of state, Antony Blinken, met mediators from Egypt and Qatar on Tuesday, even as Hamas and Israel poured cold water on any prospect of any imminent pause in the fighting in Gaza.

Netanyahu’s office said in a statement: “Israel will insist on the achievement of all of its objectives for the war, as they have been defined by the security cabinet, including that Gaza never again constitutes a security threat to Israel.”

Denying an Israeli television report, the prime minister’s office said Israel had not agreed to drop its demand to maintain troops in the Philadelphi Corridor, the border between Gaza and Egypt, an issue that has been a major sticking point.

A Hamas statement said its officials, who met the head of Palestinian Islamic Jihad about progress in the talks, reiterated key Hamas demands. These include an end to Israel’s Gaza operation, a full Israeli pullout and a deal to exchange Israeli hostages for Palestinian prisoners held by Israel.

Meanwhile in Gaza, Palestinian health officials reported at least 50 Palestinians killed by Israeli airstrikes over a 24-hour period.

The Israeli military said jets hit around 30 targets throughout the enclave including tunnels, launch sites and an observation post. It said troops killed dozens of armed fighters and seized weapons including explosives, grenades and automatic rifles.

Israel’s military campaign has killed more than 40,000 people in Gaza since October, according to Palestinian health authorities. The war began on 7 October when Hamas gunmen stormed into Israeli communities and military bases, killing around 1,200 people and abducting about 250 hostages, according to Israeli tallies.

Reuters contributed to this report

Israeli attacks on Palestinian water supplies in the occupied West Bank and Gaza Strip accounted for a quarter of all water-related violence in 2023, as armed conflicts over dwindling resources surged globally, according to new research.

Almost 350 water conflicts were documented worldwide in 2023, a 50% rise on 2022, which was also a record year, according to the Pacific Institute, a California-based nonpartisan thinktank tracking water violence. The violence included attacks on dams, pipelines, wells, treatment plants and workers, as well as public unrest and disputes over access to water, and the use of water as a weapon of war.

Overall, water-related violence has been rising steadily since 2000 but has surged in recent years as the climate crisis and growing scarcity exacerbate old conflicts over land, ideology and religion, economics and sovereignty, and new ones erupt, according to the Water Conflict Chronology. In 2000, just 20 water conflicts were documented by the tracker.

Regions with major jumps in water violence include Latin America and the Caribbean, a region hit by drought and unequal access to water resources, where year-on-year the number of incidents rose more than threefold to 48 in 2023. In Bolívar, Colombia, police fired guns and teargas to disperse residents protesting a 10-day water outage, injuring four.

Meanwhile in India, severe drought and community disputes over access to irrigation water for farmland drove a 150% increase in water conflicts last year, with 25 incidents including clashes between communities in the neighboring southern states of Tamil Nadu and Karnataka over the Cauvery River.

“All these cases highlight different aspects of the growing water crisis: the failure to enforce and respect international law; the failure to provide safe water and sanitation for all; and the growing threat of climate change and severe drought,” said Peter Gleick, co-founder of the Pacific Institute, an independent research and policy organization which created the conflict tracker in 1985.

“There was a massive uptick in violence over water in 2023, widely around the world, but especially in the Middle East.”

Water conflicts in the Middle East accounted for 38% of last year’s total, driven in large part by attacks on Palestinian water supplies and infrastructure in the occupied territories, according to the tracker, which monitors news reports, eyewitness accounts, UN reports and other conflict databases.

Israeli settlers and/or armed forces contaminated and destroyed water wells, pumps and irrigation systems on 90 occasions during 2023 – the equivalent of more than seven water-related acts of violence every month.

In Gaza, the water situation was already dire before Israel launched its war in retaliation for the deadly attack by Hamas on 7 October, after which much of the water and wastewater infrastructure in Gaza has been destroyed, damaged or left unusable.

In November, Israeli airstrikes partially destroyed solar panels and other infrastructure providing energy for the EU-supported Gaza Central wastewater treatment plant, which served 1 million people. In another attack, the Israeli military began pumping seawater into Hamas’s tunnel complex in an effort to destroy the clandestine transport and communications system, an action that risked “ruining the basic conditions for life in Gaza” – an element of the crime of genocide, a senior hydrologist told the Guardian in December.

In the West Bank, much of the water violence appeared to be linked to the annexation and settlements by Israelis that were ruled unlawful by the international court of justice in a landmark advisory opinion.

In one documented case from September, Israeli settlers from Shaarei Tikva reportedly pumped wastewater on to Palestinian agricultural lands east of Qalqilya, causing damage to olive trees and crops. In another from November, Israeli settlers reportedly demolished homes, a school’s water tanks and a water pipeline, and uprooted dozens of young olive trees in the occupied city of Hebron.

The Israeli foreign ministry has rejected the ICJ ruling as “fundamentally wrong” and one-sided. The government has been approached for comment.

Meanwhile, the number of water-related attacks in the war between Russia and Ukraine dropped by 26% compared with 2022 but remained high, with 32 reported incidents. This included Russian forces blowing up a dam on the Mokri Yaly River in mid-June 2023, causing flooding on both banks, reportedly to slow down a Ukrainian counteroffensive. In September, power lines and a water main were damaged by Ukrainian forces shelling in Gordeevka, Kursk.

“The large increase in these events signals that too little is being done to ensure equitable access to safe and sufficient water and highlights the devastation that war and violence wreak on civilian populations and essential water infrastructure,” said Morgan Shimabuku, senior researcher with the Pacific Institute.

“The new analysis exposes the increasing risk that climate change adds to already fragile political situations by making access to clean water less reliable in areas of conflict around the world.”

A doctor accused of illegally supplying ketamine to the Friends star Matthew Perry before his accidental overdose death last year plans to return to his medical practice as soon as this week.

Dr Salvador Plasencia’s attorney confirmed to NBC News that the physician plans to resume practicing at the urgent care clinic he operates in Calabasas, a city in the San Fernando valley in Los Angeles county.

Last week, Plasencia pleaded not guilty to one count of conspiracy to distribute ketamine and was released on a $100,000 bond. A judge overseeing his case ruled that he must display a sign on the door of his clinic informing potential patients of his pending court case.

Plasencia’s patients are also required to sign a form asserting that they understand the allegations against him and consent to treatment on every visit.

Prosecutors claim that Perry was injected with ketamine at least 20 times in the days before his death from intoxication and drowning in a hot tub in October of last year. In the hours before his death, he had been injected three times.

On the final occasion, Perry allegedly directed his assistant, Kenneth Iwamasa, to “shoot me up with a big one” and get the hot tub ready. The assistant gave Perry the dose and left the home to run errands, the papers say. When he returned, Perry was facedown in the water.

Prosecutors allege that Plasencia provided ketamine to Iwamasa. He is also accused of giving injections of the drug to Perry himself and teaching the assistant how to give them.

Perry had been undergoing ketamine treatments to treat depression but is believed to have sought alternative sources of the drug when the clinic involved began to restrict doses. Prosecutors said the actor had been obtaining the drug illegally outside his scheduled doses as part of an “out-of-control” addiction.

The drug is popular as an alternative treatment, with users extolling a sensation of going down a rabbit hole into an egoless state.

Iwamasa pleaded guilty to one count of conspiracy to distribute ketamine causing a death and of administering injections without medical training. According to prosecutors, Perry had a scheduled ketamine infusion with a doctor on 14 October, two weeks before he died, on 28 October.

On that day, the assistant had contacted Plasencia for more of the drug and the doctor agreed to meet at Perry’s home and administered a “large dose of ketamine”. But Perry had a reaction to the additional dose and his body began to “freeze up”.

According to Iwamasa’s plea agreement, Plasencia left additional vials of ketamine for the actor at his home. But Perry wanted more, and instructed Iwamasa to contact another supplier.

Court-released texts appear to show that Plasencia received ketamine from another physician charged in the case, Dr Mark Chavez, who previously ran a ketamine clinic. Chavez is alleged to have submitted a fraudulent prescription for ketamine for Plasencia to pass along to Perry.

Iwamasa has said he bought about $55,000 worth of ketamine in the month before Perry’s death from multiple sources including, prosecutors allege, Plasencia, the “ketamine queen” Jasveen Sangha, Chavez and drug broker Erik Fleming.

One one occasion, Chavez allegedly sold Plasencia at least four vials of liquid ketamine and ketamine lozenges for $2,000.

In a September 2023 text to Chavez, Plasencia described his visit to Perry’s home as being “like a bad movie”. After a visit to the actor’s home a month later, Plasencia wrote to Chavez: “[If] today goes well we may have repeat business.”

“Let’s do everything we can to make it happen,” Chavez allegedly replied.

Plasencia and Chavez also discussed how much to charge Perry, according to court documents. “I wonder how much this moron will pay,” Plasencia texted Chavez. Chavez allegedly replied: “Let’s find out.”

A 2,492-carat raw diamond discovered in Botswana could be the second-largest gem-quality example ever unearthed.

The Canadian mining company Lucara Diamond Corp said it had recovered the “exceptional” stone from its Karowe diamond mine, with a photo showing the hefty rough diamond sitting in the cupped palm of a hand.

The largest gem-quality diamond ever discovered was the 3,106 carat Cullinan diamond, which was mined in South Africa in 1905 when it was still a British colony and gifted to King Edward VII. It was cut up into several gems, some of which are now part of the Crown Jewels.

Lucara’s president, William Lamb, said: “We are ecstatic about the recovery of this extraordinary 2,492-carat diamond.”

Lucara did not say what the value of the “high quality” diamond was or if it could be cut into gems. Botswana’s government said it was the biggest diamond discovered in the country.

Its Karowe mine has been yielding progressively bigger stones. In 2019, Lucara dug out the 1,758-carat Sewelo diamond, then the world’s second-biggest mined diamond. Louis Vuitton bought it for an undisclosed sum, even though it was black in appearance and it was unclear how many gems could be cut from it.

The 1,111-carat Lesedi La Rona diamond, also from Karowe, was bought by a British jeweller for $53m (£40m) in 2017.

The largest diamond ever found was the black Sergio stone, which was discovered above ground in Brazil in 1895 and cut up to be used in industrial drills. Black “carbonado” stones such as the Sergio are thought to be parts of meteorites.

Russia is the world’s largest diamond producer, but most large valuable finds have been made in Botswana in recent years. The southern African country has been trying to increase its power in the industry, negotiating a progressively bigger share of stones mined by Anglo American-owned De Beers last year, in a new 10-year agreement.

Botswana’s president, Mokgweetsi Masisi, will be one of the first people to see Lucara’s new, as yet unnamed, diamond before it is shown to the world at his office, the government said.

Both of Canada’s major rail freight companies have shut down their rail networks in the country and locked out nearly 10,000 workers after unsuccessful negotiations with a major union.

The decision, confirmed by the Teamsters union, sets the stage for an unprecedented rail stoppage that could badly damage the Canadian economy and have a significant effect on cross-border trade with the US.

Canada is the world’s second-largest country by area and relies heavily on rail transport. The stoppage is expected to cripple shipments of grain, potash and coal while also slowing the transport of petroleum products, chemicals and vehicles.

Industry groups had urged Justin Trudeau’s Liberal government to prevent a stoppage, noting Canada’s railways transport about C$380bn (£214bn) worth of goods annually.

Canadian National Rail (CN) and Canadian Pacific Kansas City (CPKC) began lockouts on Thursday morning after tense negotiations following complaints from workers over worsening job conditions failed to produce a deal.

CN confirmed it had moved ahead with the lockout, saying the union “did not respond to another offer by CN in a final attempt to avoid a labour disruption”. It said: “Without an agreement or binding arbitration, CN had no choice but to finalise a safe and orderly shutdown and proceed with a lockout.”

The union said: “Despite months of good faith negotiations on the part of the Teamsters Canada Rail Conference, parties remain far apart, and both CN and CPKC have began their lockout of 00:01 today … Despite the lockout, the Teamsters remain at the bargaining table with both companies.”

In its announcement, CPKC said: “The TCRC [union] leadership continues to make unrealistic demands that would fundamentally impair the railway’s ability to serve our customers with a reliable and cost-competitive transportation service.”

A pause to freight traffic will have cascading effects on Canada and the US. According to the Railway Association of Canada, affected rail carries more than C$1bn worth of goods each day. Nearly half the aviation fuel used at Toronto’s Pearson airport, Canada’s busiest air terminal, arrives by rail. More than 32,000 commuters in Montreal, Vancouver and Toronto rely on the rail network. A strike would also hit the mining, agriculture and retail industries.

The federal labour minister, Steven MacKinnon, said on Wednesday night that he had completed meetings with the companies and the Teamsters union. He called for urgency at the negotiating table and for a deal to be done.

In recent days, the Calgary-based CPKC and Montreal-based CN had started winding down operations. In Canada, both companies, valued at roughly C$100bn each, own virtually all of the rail track in the country and control most of the freight shipment. The country has never experienced a labour stoppage involving both companies simultaneously.

As the possibility of a strike loomed, industry groups issued a joint statement calling on the government to intervene, saying it “has a responsibility to protect the Canadian public and maintain national security, and it is time to act decisively to fulfil that obligation”.

MacKinnon last week declined a request from CN and CPKC to move negotiations to binding arbitration. “These collective bargaining negotiations belong to CN Rail, CPKC and [Teamsters] workers alone – but their effects will be borne by all Canadians,” he said.

On Wednesday, Trudeau said the country’s two main rail companies and the Teamsters union had to settle their differences at the negotiating table, but stopped short of suggesting his government might get involved.

“My message is very straightforward. It is in the best interest of both sides to continue doing the hard work at the table to find a negotiated resolution,” the prime minister said. “Millions of Canadians, of workers, of farmers, of businesses right across the country are counting on both sides to do the work and get to a resolution.”

The deputy prime minister, Chrystia Freeland, said: “We know that the best deals are reached at the bargaining table, and I am calling with extreme seriousness on the employers and on the union to roll up their sleeves to get a deal done.”

The union representing workers at CPKC said the company wanted to “gut the collective agreement of all safety-critical fatigue provisions” while those with CN said the rail operator wanted work days to be extended in western provinces, potentially creating “a fatigue-related safety risk”. The unions have cited fatigue management, rest periods and scheduling as key sticking points.

Both companies said offers on the table were competitive and did not compromise safety.

Reuters contributed to this report

Both of Canada’s major rail freight companies have shut down their rail networks in the country and locked out nearly 10,000 workers after unsuccessful negotiations with a major union.

The decision, confirmed by the Teamsters union, sets the stage for an unprecedented rail stoppage that could badly damage the Canadian economy and have a significant effect on cross-border trade with the US.

Canada is the world’s second-largest country by area and relies heavily on rail transport. The stoppage is expected to cripple shipments of grain, potash and coal while also slowing the transport of petroleum products, chemicals and vehicles.

Industry groups had urged Justin Trudeau’s Liberal government to prevent a stoppage, noting Canada’s railways transport about C$380bn (£214bn) worth of goods annually.

Canadian National Rail (CN) and Canadian Pacific Kansas City (CPKC) began lockouts on Thursday morning after tense negotiations following complaints from workers over worsening job conditions failed to produce a deal.

CN confirmed it had moved ahead with the lockout, saying the union “did not respond to another offer by CN in a final attempt to avoid a labour disruption”. It said: “Without an agreement or binding arbitration, CN had no choice but to finalise a safe and orderly shutdown and proceed with a lockout.”

The union said: “Despite months of good faith negotiations on the part of the Teamsters Canada Rail Conference, parties remain far apart, and both CN and CPKC have began their lockout of 00:01 today … Despite the lockout, the Teamsters remain at the bargaining table with both companies.”

In its announcement, CPKC said: “The TCRC [union] leadership continues to make unrealistic demands that would fundamentally impair the railway’s ability to serve our customers with a reliable and cost-competitive transportation service.”

A pause to freight traffic will have cascading effects on Canada and the US. According to the Railway Association of Canada, affected rail carries more than C$1bn worth of goods each day. Nearly half the aviation fuel used at Toronto’s Pearson airport, Canada’s busiest air terminal, arrives by rail. More than 32,000 commuters in Montreal, Vancouver and Toronto rely on the rail network. A strike would also hit the mining, agriculture and retail industries.

The federal labour minister, Steven MacKinnon, said on Wednesday night that he had completed meetings with the companies and the Teamsters union. He called for urgency at the negotiating table and for a deal to be done.

In recent days, the Calgary-based CPKC and Montreal-based CN had started winding down operations. In Canada, both companies, valued at roughly C$100bn each, own virtually all of the rail track in the country and control most of the freight shipment. The country has never experienced a labour stoppage involving both companies simultaneously.

As the possibility of a strike loomed, industry groups issued a joint statement calling on the government to intervene, saying it “has a responsibility to protect the Canadian public and maintain national security, and it is time to act decisively to fulfil that obligation”.

MacKinnon last week declined a request from CN and CPKC to move negotiations to binding arbitration. “These collective bargaining negotiations belong to CN Rail, CPKC and [Teamsters] workers alone – but their effects will be borne by all Canadians,” he said.

On Wednesday, Trudeau said the country’s two main rail companies and the Teamsters union had to settle their differences at the negotiating table, but stopped short of suggesting his government might get involved.

“My message is very straightforward. It is in the best interest of both sides to continue doing the hard work at the table to find a negotiated resolution,” the prime minister said. “Millions of Canadians, of workers, of farmers, of businesses right across the country are counting on both sides to do the work and get to a resolution.”

The deputy prime minister, Chrystia Freeland, said: “We know that the best deals are reached at the bargaining table, and I am calling with extreme seriousness on the employers and on the union to roll up their sleeves to get a deal done.”

The union representing workers at CPKC said the company wanted to “gut the collective agreement of all safety-critical fatigue provisions” while those with CN said the rail operator wanted work days to be extended in western provinces, potentially creating “a fatigue-related safety risk”. The unions have cited fatigue management, rest periods and scheduling as key sticking points.

Both companies said offers on the table were competitive and did not compromise safety.

Reuters contributed to this report

The British tech entrepreneur Mike Lynch has been confirmed dead by search and rescue authorities after his yacht sank off the coast of Sicily during a violent storm, according to officials.

Lynch, 59, the founder of Autonomy Corporation, was among six people missing after the British-flagged 56-metre sailing boat Bayesian capsized at about 5am local time on Monday off the coast of Palermo when the area was hit by a tornado.

Lynch’s body was retrieved from the wreck on Thursday, Massimo Mariani, an interior ministry official, told Reuters after being briefed by the emergency services. Agence France-Presse also reported that Lynch’s body had been recovered, citing a coastguard official.

His wife, Angela Bacares, was rescued on Monday, while his 18-year-old daughter, Hannah, is still unaccounted for.

Lynch’s daughter is still missing, Mariani said. He said she may be inside the wreck or could have been tossed into the sea as the boat sank.

A spokesperson for the Italian fire brigade said it could take days before the last missing person was found, given the difficulties facing the divers on a wreck that is 50m (165ft) below the surface.

The bodies of four people were recovered from the wreck on Wednesday. The body of the yacht’s chef, Recaldo Thomas, was found on Monday, shortly after the vessel sank.

Once described as Britain’s Bill Gates, Lynch spent much of the last decade in court defending his name against allegations of fraud related to the sale of Autonomy to the US tech company Hewlett-Packard for $11bn (£7bn).

He was acquitted by a jury in San Francisco in June after he had spent more than a year living in effect under house arrest. The boat trip was a celebration of Lynch being cleared of the charges.

Lord Browne, the chair of the Francis Crick Institute, was among the first to pay tribute to Lynch. In a post on X, he wrote: “Mike Lynch should be remembered as the person who catalysed a breed of deep tech entrepreneurs in the UK.

“His ideas and his personal vision were a powerful contribution to science and technology in both Britain and globally. I send my condolences to those close to him. We have lost a human being of great ability.”

Lynch was a member of the Create the Change fundraising board, set up by Cancer Research UK and which helped fund the building of the institute. He was also a director of the BBC for five years.

David Tabizel, Lynch’s co-founder at Autonomy, posted on X: “It looks like we’ve lost our dear Dr Mike Lynch. RIP. The world has lost a genius. His family have lost a giant of a man.”

The Royal Academy of Engineering, where Lynch was a fellow, said in a statement that it was deeply saddened by his death: “Mike became a fellow of the Royal Academy of Engineering in 2008 and we have fond memories of the active role he played in the past, as a mentor, donor and former council member. He was also one of the inaugural members on the enterprise committee. Our thoughts are with his family and friends at this time.”

Tim Davie, BBC director general, paid tribute to Lynch on Thursday. He said: “We are deeply saddened by the awful news about the deaths of those aboard the Bayesian yacht. Mike Lynch was an outstanding BBC director, who made a major contribution during his time on the board, from 2007 to 2012.

“Wise, generous and insightful, he played a particularly key role in accelerating our transformation as a digital organisation. Our thoughts are with his family and all others involved.”

Earlier on Thursday, a senior official confirmed to the Guardian that divers had recovered a fifth body from the wreck. The head of Sicily’s civil protection agency, Salvatore Cocina, said the fifth body inside the yacht had been successfully recovered and transported to Porticello’s pier.

Italian media, quoting sources among the divers, said the victims retrieved on Wednesday were Chris Morvillo and his wife, Nada, as well as the executive chair of Morgan Stanley International, Jonathan Bloomer, and his wife, Judy. The Bloomers’ family described them as “incredible people and an inspiration to many”.

The bodies recovered on Wednesday were taken to hospitals in the nearby city of Palermo. They have not been officially identified.

There were 22 people onboard when the yacht sank. Fifteen survived, including a one-year-old girl.

Six African cities will have more than 10 million people by 2035, with the continent’s booming young population making it the world’s fastest urbanising region, according to a report.

Angola’s capital, Luanda, and Tanzania’s commercial hub, Dar es Salaam, will join the metropolises of Cairo, Kinshasa, Lagos and Greater Johannesburg with populations of more than 10 million, the Economist Intelligence Unit said in a report on African cities.

Africa’s youthful, growing cities are seen as a boundless source of creativity and innovation, but many have also been the focus of waves of protests this year amid corruption, tax rises, a lack of jobs and political classes that are more often than not regarded as out of touch.

This fast-paced urbanisation, which will result in more than half of Africans living in towns and cities by 2035, is expected to create wealth, dynamism and business opportunities, the report says.

But, it adds: “Overcrowding, informal settlements, high unemployment, poor public services, stretched utility services and exposure to climate change are just some of the major challenges that city planners will have to grapple with.”

By 2035, on top of the six megacities, the continent will have 17 urban areas with more than 5 million people and about another 100 with more than 1 million.

Of the 100 largest cities by 2035, Addis Ababa is expected to grow at an average annual rate of 10.6%, followed by Kampala, Dar es Salaam and Abidjan at above or near 9%.

The continent’s urban population is forecast to reach almost 1 billion by 2035, up from about 650 million last year. East Africa is expected to be the region with the fastest growing urban population, followed by central Africa and west Africa.

The EIU said “megalopolises in the making” include a 370-mile (600km) stretch of west Africa’s coast from Abidjan, in Ivory Coast, east through Ghana, Togo and Benin to Lagos, in Nigeria, which “could become one of the world’s largest urban corridors by 2035”, with more than 50 million people.

Other potential megalopolises it identified centre on Cairo and Alexandria, in Egypt; Johannesburg and Pretoria, in South Africa; a “Great Lakes city hub” encompassing Nairobi, in Kenya, and Kampala, in Uganda; and clusters in Morocco and Algeria.

The UN estimates that Africa’s population will almost double in the next 30 years, to 2.2 billion. About 70% of the population is under the age of 30.

Researchers have found a soft and squidgy water-rich gel is not only able to play the video game Pong, but gets better at it over time.

The findings come almost two years after brain cells in a dish were taught how to play the 1970s classic, a result the researchers involved said showed “something that resembles intelligence”.

The team behind the latest study said that while they were inspired by that work, they were not claiming their hydrogel was sentient.

“We are claiming that it has memory, and through that memory it can improve in performance by gaining experience,” said Dr Vincent Strong, the first author of the research, from the University of Reading.

Strong said the work could offer a simpler way to develop algorithms for neural networks – models that underpin AI systems including Chat GPT – noting that at present they are based on how biological structures work.

Released in 1972, Pong was one of the first video games and has a simple premise: two paddles on a court can be moved up and down to hit a ball back and forth between them. The longer the rally, the higher the score.

Strong’s study focused on a single-player version in which a paddle is moved along one wall of a court to keep a ball bouncing around.

Writing in the journal Cell Reports Physical Science, he and his colleagues describe how they sandwiched an electroactive polymer hydrogel between two plates, each bearing a 3×3 array of electrodes hooked up to a computer system that simulated Pong.

Six of the electrode pairs, in a 3×2 arrangement, were then stimulated to represent the movement of the ball within the game’s court.

Across the other three electrode pairs – representing the wall along which the paddle is located – the team applied a small voltage and the current was measured with sensors. The position of the paddle was defined as the point where the current was highest.

Crucially, the type of hydrogel used in the experiment contains charged ions. These move in response to electrical stimulation and linger where they end up.

As a result, the point along the “wall” with the highest current could shift as the ball moved, meaning the paddle could change position.

“At the beginning the ions are equally and randomly distributed so the paddle hits and misses the ball,” said Strong.

But as the ball bops around the court, the gel receives more and more electrical stimulation.

“Over time the ion concentrations increase where the ball is most, acting as a kind of muscle memory, as with the higher concentrations there are higher electric current readings and the paddle is able to act more accurately,” said Strong.

In other words, the paddle is able to hit the ball more often, resulting in longer rallies.

“Our research shows that even very simple materials can exhibit complex, adaptive behaviours typically associated with living systems or sophisticated AI,” said Dr Yoshikatsu Hayashi, another author of the research at the University of Reading.

Dr Brett Kagan, the chief scientific officer at Cortical Labs, who worked on the Pong-playing brain cells but was not involved in the latest study, said the hydrogel system demonstrates a basic form of memory similar to the way a riverbed records a memory of the river.

That, he said, can be useful to understand how changes within a medium may help electrical signals travel through it better.

But he said significantly more work would be needed to show hydrogels can “learn”.

“The performance and the improvement was tied to a specific location of stimulation. When this was changed in any way the system was not able to reorganise to still show performance,” Kagan said.

“This is different to our tests in neural systems where we showed that regardless of how you presented the information, learning still occurred.”

The auditor PwC China has reportedly told clients that it expects to receive a six-month ban from Chinese authorities, and potentially a large fine, as a punishment for its role in auditing the collapsed property developer Evergrande.

PwC expects to be banned from conducting regulated activities in China, such as signing off on financial results, for six months starting in September, the Financial Times reported.

In March, Beijing’s securities regulator said that Evergrande, the world’s most indebted property developer before it collapsed in January, had inflated its revenues by almost $80bn (£61.6bn) in 2019 and 2020. Evergrande was ordered to pay a $580m fine for the alleged fraud. Its founder, Hui Ka Yan, was detained by the authorities in September and ordered to pay a $6.5m fine.

Evergrande’s downfall led to scrutiny of PwC China, which had audited the property developer’s accounts for 14 years until 2023.

The FT cited an unnamed former partner at PwC, which has more than 20,000 employees in mainland China, as saying: “The current partners are braced for impact.”

PwC China is the most prominient of the “big four ” accounting firms, a term that includes Deloitte, KPMG and EY, operating in China. In 2022, it generated nearly 8bn yuan in revenues, according to the Chinese Institute of Certified Public Accountants.

However, in recent months, amid heightened scrutiny of PwC China’s links to Evergrande, the auditor has been shedding clients. This week, its biggest mainland China-listed client, Bank of China, said it planned to switch to EY. China Life Insurance, China Telecom and PICC have also dropped PwC as a client, according to Reuters.

The regulatory action on the horizon for PwC China is expected to eclipse the punishment received last year by Deloitte, which paid a $31m fine and was suspended for three months in relation to its audit of China Huarong Asset Management.

State-owned companies in China are generally banned from hiring auditors within three years of an auditor receiving a significant regulatory punishment. In February last year it was reported that Beijing had instructed state-owned companies to phase out contracts with the big four accounting firms, as authorities tried to address security concerns and curb the influence of western-linked auditors.

PwC China said: “Given this is an ongoing regulatory matter, it would not be appropriate to comment.”

A Brazilian migrant living in Spain has been hailed as a hero after he risked his own life to rescue a young child who was dangling precariously off a second-floor balcony in the coastal city of Alicante.

Felipe David Souza, a 29-year-old painter, was preparing to head home on Wednesday when he heard screams outside the apartment where he was working. He glanced out and saw that a crowd of people had gathered on the street below.

Many were frantically pointing to the balcony next to where he was working. “I saw a little boy with half his body out,” Souza later told reporters.

The six-year-old child was seemingly frozen with fear on the railing of the balcony, one leg dangling over the metres-high drop. Below the crowd was desperately yelling at the young boy, telling him to climb back inside.

Video filmed at the scene shows Souza swiftly swinging himself over the balcony railing, gripping the rail tightly as he began inching his way along the narrow ledge towards the child. “I did it without thinking,” he said.

The owner of a nearby cafe, Inés Su, was among those anxiously watching the rescue from below. Neighbours had called police and had begun hauling cushions out on the street in case the child fell, she told reporters. They watched as Souza appeared, seemingly out of nowhere. “We all had our hearts in our throats.”

High above, Souza worried that his approach would startle the child. “I was staring at the child to keep him calm, willing him not to move,” he said. “It’s a short distance but it felt so long.”

Video shows Souza calmly inching towards the child, gently grabbing his shirt as he guided the child back over the railing. A sigh of relief rippled through the crowd below as they burst into applause.

Souza said he had been thanked by the shocked parents who told him that they had dozed off when the child managed to open the window and slip out in a matter of seconds. “I’m really happy that the child is safe,” said Souza. Neighbours described the family as French tourists.

On Thursday, an official from Alicante’s city council told Souza that the municipality was planning to recognise his bravery in an award ceremony in November. “You risked your life to save that of the minor,” the councillor Julio Calero told him, describing Souza’s intervention as a “heroic act of immeasurable value”.

Souza has lived in Spain for nine years, he told the local news site Información.es. “Of course, I’ve suffered racism on several occasions since I arrived but you can’t pay attention to these things.”

He had no doubt, however, that he would make the same choice if he was ever again faced with the same situation. “Of course, I would do it 50 times over if I had to,” he said. “I’m a parent myself, so all I could think about was how I wanted nothing bad to happen to the child.”