France, Spain and other western European nations braced on Saturday for a sweltering June weekend that is set to break records and sparked concern about forest fires and the effects of climate change.
Temperatures already nudged over 40 degrees Celsius in parts of France on Friday.
Temperatures are due to relent slightly from Sunday with thunderstorms forecast in parts of France and elsewhere in Europe.
But French state weather forecaster Meteo France said June temperature records had already been beaten in 11 areas on Friday and could reach as high as 42 Celsius in some areas on Saturday.
In Spain, forest fires burned nearly 9,000 hectares (22,240 acres) of land in the northwest Sierra de la Culebra region Friday, forcing some 200 people from their homes, regional authorities said.
And more than 3,000 people were evacuated from the Puy du Fou theme park in central Spain due to a fierce fire nearby.
Firefighters were battling fires in several other regions, including woodlands in Catalonia where weather conditions complicated the fight.
Spanish Prime Minister Pedro Sanchez praised firefighters "who risk their lives on the frontline of fires" on Friday, which is also World Day to Combat Desertification and Drought.
Temperatures were above 35 Celsius (95 Fahrenheit) Friday in most parts of the country.
More than half of French departments were at the highest or second-highest heat alert level by the afternoon on Friday.
"Hospitals are at capacity, but are keeping up with demand," Health Minister Brigitte Bourguignon told reporters in Vienne, near Lyon in the southeast.
Schoolchildren were told to stay at home in departments at alert level "red" and the health ministry activated a special heatwave hotline.
The Red Cross also organised efforts to distribute fresh water to the homeless community in Toulouse, where temperatures are expected to soar to 38 Celsius on Saturday.
"There are more deaths of people in the streets in the summer than in the winter," said volunteer Hugues Juglair, 67.
Meanwhile rock and metal fans at the music festival Hellfest in western France were sprayed with water from hoses and enormous vaporisers in front of the stage as they headbanged or bounced to an opening-day line-up including Deftones and The Offspring.
"This is the earliest heatwave ever recorded in France" since 1947, said Matthieu Sorel, a climatologist at Meteo France.
With "many monthly or even all-time temperature records likely to be beaten in several regions," he called the weather a "marker of climate change".
Several towns in northern Italy have announced water rationing and the Lombardy region may declare a state of emergency as a record drought threatens harvests.
The UK recorded its hottest day of the year on Friday with temperatures reaching over 30 Celsius in the early afternoon, meteorologists said.
It was the third day in a row that temperature records had been broken in the UK, where it was over 28 Celsius on Wednesday and 29.5 Celsius on Thursday.
Experts warned that the high temperatures were caused by worrying climate change trends.
"As a result of climate change, heatwaves are starting earlier," said Clare Nullis, a spokeswoman for the World Meteorological Organization in Geneva.
"What we're witnessing today is unfortunately a foretaste of the future" if concentrations of greenhouse gases in the atmosphere continue to rise and push global warming towards 2 Celsius from pre-industrial levels, she added.
In France, special measures have been taken in care homes for elderly people, still haunted by the memory of a deadly 2003 heatwave.
Buildings are being sprayed down with water to cool them and residents are being rotated through air-conditioned rooms.
In the Gironde department, which includes Bordeaux, authorities said all public events outdoors or in non-air-conditioned venues would be banned from 2:00 pm (1200 GMT) on Friday, a measure set to be broadened across the region.
And speed limits in several regions, including around Paris, have been reduced to limit the concentration of harmful smog or ozone in the heat.
Paris police chief Didier Lallement said only the least polluting vehicles would be allowed to drive in the capital on Saturday due to fine particle pollution.
Electric grid operator RTE said increased use of fans and air-conditioners was also driving up power consumption.