France has had its hottest day, 45.1C in the small southern town of Villevieille, as across Europe authorities checked on tourists, schools and hospitals.
Schools are dousing pupils with water and nursing homes are equipping the elderly with hydration sensors as Europe battles a record-setting heatwave.
Several people have died across the continent in incidents authorities are linking to the exceptional weather.
A major wildfire is raging in northeastern Spain, sparked after a pile of chicken dung spontaneously combusted in the heat.
Several countries have reported record temperatures this week, and France hit its all-time heat record on Friday: 45.1C in the small southern town of Villevieille, according to French media.
The French national weather service activated its highest level heat danger alert for the first time, putting four regions around Marseille and Montpellier in the south of the country under special watch.
About 4000 schools closed because they could not ensure safe conditions, and local authorities cancelled many end-of-school-year carnivals.
Some criticised the government for going overboard but Prime Minister Edouard Philippe defended the efforts after 15,000 people died in a heatwave in 2003 that woke France up to the risks.
"This heatwave is exceptional by its intensity and its earliness," he told reporters.
"Measures have been taken for the most vulnerable people. But given the intensity of the heatwave, it's the entire population who must be careful today ... both for oneself and for loved ones and neighbours."
Italy put 16 cities under alerts for high temperatures, and civil security services distributed water to tourists visiting famed sites around Rome under a scorching sun.
Heat was blamed for the deaths of two people in Spain, private news agency Europa Press reported.
An 80-year-old man collapsed and died in the street in Valladolid, in northwest Spain, the agency said, and a 17-year-old boy died in the southern city of Cordoba after diving into a swimming pool and losing consciousness.
Four people have drowned so far in France this week. The health minister warned people to swim only in authorised areas.
France has also seen a rise in so-called street-pooling, or illegally opening fire hydrants. A six-year-old child is in life-threatening condition after being hit by water shooting from a hydrant in the Paris suburb of Saint-Denis, broadcaster France-Info reported.
More than 700 firefighters and six water-dropping aircraft are battling the worst fire in two decades in the Catalonia region as Spain is forecast to endure the peak of its heatwave, with temperatures expected to exceed 40C.
Authorities in Spain said more than 700 firefighters, eight helicopters and six water-dropping aircraft aimed to slow the progress of a wildfire until nightfall, when cooler temperatures might give them an advantage.
A stiff breeze was driving the flames in the direction of Lleida, 30km away, although officials said the city was not considered to be under threat.
Temperatures in the area of the fire reached 41C but were forecast to drop from Saturday.
Authorities are caring for more than 50 people evacuated the previous day. They included locals as well as people from Britain, Belgium, Germany, Brazil and the US, according to Europa Press.
In Berlin, a police unit turned water cannons - usually used against rioters - on city trees to cool them down.
The World Meteorological Organisation said 2019 was on track to be among the world's hottest years, and that 2015-2019 would then be the hottest five-year period on record.
It said the European heatwave was "absolutely consistent" with extremes linked to the impact of greenhouse gas emissions.