France recorded its hottest day ever on Tuesday amid an exceptional heatwave, the national weather agency said.Meteo France said the country’s national thermal indicator – an average of temperatures measured at 30 weather stations – hit a new record of 29.8C. The previous record of 29.4C dated back to heatwaves of August 2003 and July 2019.Temperature records also tumbled at individual weather stations and on consecutive days in some towns as daytime highs climbed well above 40C.The national weather service placed 54 areas of France under a red heatwave alert.Forty people have drowned while swimming in unsupervised areas across France in recent days, the prime minister has said.“There is a tragic scourge of drownings,” Sébastien Lecornu said on Tuesday. “The latest figures we’ve received are 40 deaths since June 18th. Most of the victims are young people.”Lecornu was preparing to chair a crisis meeting with ministers to address the ferocious early summer heatwave.The heat was believed to be linked to the deaths of two young children in their family car on Monday. First responders were unable to resuscitate two children, aged two and four, who were found unconscious ‌by ‌their mother ​in the family car outside their home, said a prosecutor in Carpentras, southeast France.The national weather service, Météo-France, said on Tuesday that 54 departments had been placed under a red heatwave alert as “oppressive and exhausting” heat smothered about half of the country. It said overnight temperatures were the hottest since record-keeping began in 1947.A pharmacy sign displays the temperature in Beziers, southern France. Photograph: Gabriel Bouys/AFP/Getty Images Officials in the greater Paris region advised people to work from home as much as possible and avoid rail journeys. Meteo France said the heatwave has reached what it described as a “plateau of severity”, with unrelenting heat, day and night. A growing number of regions will tip into the red again on Wednesday as the heat spreads across more than half of the country, including the northernmost tip of France, the weather service said.Human-caused climate change is tied to increasing extreme weather and UN climate agency projections suggest the next five years will shatter more heat records.“Further record-breaking temperatures are expected, including some that could surpass all previous records, regardless of the time of year,” Météo-France said.The sweltering temperatures extending across swathes of Europe are caused by what Clair Barnes, a climate scientist at Imperial College London, described as a bulging mass of hot air.“It’s drawing warm air up from North Africa, from the Sahara, and that’s why we have this really intense heat,” Barnes told Reuters. “It’s very slow moving and it means there’s kind of no wind, ‌no breeze for respite.”In England, some schools closed early on Tuesday as the UK braced for the heatwave to set new records. With temperatures expected to rise to 40 degrees, the Met Office issued its second ever red heat warning. The UN secretary general, António Guterres, said in an address to a London Climate Action Week event on Tuesday: “London isn’t just calling. It’s cooking.” He urged the world to work towards limiting global warming. “A climate crisis is pushing us deeper towards higher temperatures and closer to catastrophic tipping points, and an energy crisis is exposing the folly of a world hooked on hydrocarbons,” he said. In Italy, the health minister declared a red heatwave alert in 15 cities including Milan and Rome. In Germany, officials said swimming accidents had spiked over the weekend, leading to the deaths of five people.Nearly all of Spain was under a heat alert on Tuesday, with red alerts warning of “extraordinary danger” issued for areas around the southern city of Córdoba, the northern city of Bilbao and parts of the northern region of Cantabria.Spain’s national weather service, Aemet, issued red alerts for temperatures of 44C in southern Andalusia as well as warnings of 40C in the normally temperate Cantabria and the Basque Country regions along its northern Atlantic coast.Aemet meteorologist Rubén del Campo said Spain, which has experienced increasingly torrid summers of late, is only going to get hotter because of climate change as heatwaves become more frequent, longer and appear outside the traditional window of July and August.People shelter from the sun at Parliament Square, central London. Photograph: Jordan Pettitt/PA Wire