Here are the latest developments in Europe's heatwave.
Scientists have shown that recurring heatwaves are a clear marker of global warming, and warn they are set to become more frequent, longer and more intense.
France's electricity utility EDF shut down two more nuclear reactors -- bringing the total to three -- as extreme heat raised river temperatures and restricted the plants' ability to discharge cooling water without exceeding environmental limits designed to protect plant and animal life.
Switzerland said it was reducing operations at its Beznau plant and would shut down reactors if the heat persisted, giving similar reasons.
A three-year-old boy died after becoming trapped in his family's unlocked car in the Paris suburbs, a public prosecutor said, after two similar deaths during the extreme weather this week.
The boy was supposed to be napping but escaped his parents' supervision for at least 45 minutes, and climbed into the car. He was unable to get out because child locks on the doors were activated.
The heatwave could be linked to 212 deaths in Spain between Sunday and Wednesday, according to estimates from the MoMo monitoring system, which compiles daily death statistics and compares them with historical records.
At least 101 million people in Europe are expected to experience temperatures in excess of 35C on Thursday, including 50 million in France and 18 million in Germany, according to AFP calculations.
The heatwave is "the latest price to pay for fossil fuel pollution baking our planet", said UN climate chief Simon Stiell.
"Until humanity stops burning colossal amounts of coal, oil and gas, extreme heat will keep getting worse," Stiell said in a statement.
France will begin lifting its red alerts from Thursday evening, forecaster Meteo France said.
"On Friday, a gradual drop in temperatures along the Atlantic coast is beginning to take shape following Thursday evening's stormy conditions," the agency added.
Open-air sports events have been cancelled in Germany due to the high temperatures, with most of the country facing highs of 35 to 41C.
Experts say the current German record for June of 39.6C, recorded in 2019 in Saxony-Anhalt state, could easily be broken over the weekend.
Rail operator Deutsche Bahn warned customers not to travel because of the risk of delays and disruption from wildfires and thunderstorms.
Paris mayor Emmanuel Gregoire said there had been an "increase in mortality" in the capital owing to the heatwave, without giving figures.
He said "pretty much all our indicators are in a critical state", including calls to emergency medical services, calls to the fire brigade, ER admissions, and deaths, he told local TV.
Three deaths in northern France's Pas-de-Calais region were "likely" caused by the heatwave, the local authorities said.
They include an elderly man who was working outside and two people who died indoors and had "other medical conditions", it said.
Around 20 activists entered a pool in a Brussels park on Wednesday to protest the absence of designated outdoor swimming areas in the Belgian capital, calling it an aberration in the midst of a heatwave.
The UK recorded its hottest ever June temperature on Wednesday with the mercury rising to 36.1C in southern England, breaking the previous record of 35.6C set in 1976.
It is the second month in a row that Britain has broken historical temperature records, as scientists warn that climate change is making extreme weather events like heatwaves more frequent and intense.
A red warning for extreme heat was extended until Friday night.
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