France and Spain, among the countries worst hit, began counting the toll from the extreme temperatures, including a three-year-old boy who was trapped in his family's car. Read moreParis dream turns to nightmare as rooftop dwellers bake in historic heatwave AFP calculations based on forecasts from the German weather service and 2025 population projections from the European Joint Research Centre indicated that more than 380 million people would face temperatures of over 30C. The UN's climate chief Simon Stiell said the heatwave -- made worse by buildings and infrastructure unsuited to such temperatures -- "has the fingerprints of the climate crisis all over it". "It's the latest price to pay for fossil fuel pollution baking our planet. Until humanity stops burning colossal amounts of coal, oil and gas, extreme heat will keep getting worse," he added. The deputy director of the EU's Copernicus Climate Change Service, Samantha Burgess, said the hot weather was due to a "heat dome" of trapped air from north Africa in a low-lying high-pressure system, preventing cooler air from moving in.

More than two-thirds of Europe is facing temperatures over more than 30C © Alberto PIZZOLI / AFP

"While heat domes are a natural weather phenomenon, anthropogenic climate change is making heatwaves more severe and more likely to reach record-breaking temperatures," she added. Most of mainland France was under extreme heat alerts on Thursday, with some 63 million people out of a total population of 67 million facing temperatures of over 30C. The heat will also surpass 30C for 70 million people in Germany, 48 million in Italy and 38 million in the UK, with high temperatures also in Belgium, Luxembourg and the Netherlands. Temperatures are expected to fall in western Europe from Friday but eastern Europe was on red alert as temperatures climbed into the weekend. Cooling off In Spain, where new temperature records have been set for June, the MoMo monitoring system of mortality rates said 212 deaths between Sunday and Wednesday could be linked to the heat. Three deaths in northern France's Pas-de-Calais region were "likely" caused by the heat while a three-year-old boy was found dead in a car in the suburbs of Paris, where temperatures topped 40C on Wednesday.