Several people have died around the continent in incidents that authorities are linking to the weather. A major wildfire raged Friday in Spain, sparked when a pile of chicken dung spontaneously combusted in the heat.
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 Friday.
About 4,000 schools were closed because they couldn't ensure safe conditions.
Local authorities canceled several cultural and sport events and many end-of-school-year carnivals.
City halls were also sending volunteers to visit elderly people at home to ensure they had fans and water.
In Issy-Les-Moulineaux, a southwest Paris suburb, Jean-Jacques Emerjian, 87, and his wife Marie-France, 80 were relieved to see the Red Cross volunteers.
Marie-France Emerjian said "with my handicapped husband I am worried because I don't have someone who can come right away (to help). He fell the other night and I couldn't get him up and I was scared. He had a malaise, he fainted."
In the northern Paris suburb of Saint-Denis, the Salvation Army day center, which allows migrants living in the streets to take showers, also provided them with lots of bottled water.
Paris city hall estimates that about 1,000-2,000 migrants currently live in makeshift camps, which are particularly exposed to the heat.
Some criticized the government for going overboard, but Prime Minister Edouard Philippe defended the efforts after 15,000 people died in a heat wave in 2003 that woke up France to the risks.
"This heat wave is exceptional by its intensity and its earliness," he told reporters.
"Measures have been taken for the most vulnerable people," he said "But given the intensity of the heat wave, it's the entire population who must be careful today ... both for oneself and for loved ones and neighbors."
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 Friday.
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, and a 12-year-old girl drowned in a river near Manchester, England. France's health minister and British police warned people to swim only in authorized areas.
France has also seen an uptick in so-called street-pooling, or illegally opening fire hydrants. A 6-year-old child is in life-threatening condition after being hit by water shooting from a cracked-open fire hydrant in the Paris suburb of Saint-Denis, broadcaster France-Info reported.
More than 200 firefighters dealt with dozens of fires in the Gard region, in southeastern France, and a highway was closed for safety reasons.
More than 600 firefighters and six water-dropping aircraft were battling the worst fire in two decades in the Catalonia region Friday, as Spain is forecast to endure the peak of its heat wave, with temperatures expected to exceed 40 C (104 F).
In Berlin, a police unit turned water cannons — usually used against rioters — on city trees, to cool them down.
The World Meteorological Organization said Friday that temperature records for this time of year have been broken in Germany, France, Spain, Switzerland and Austria.
Speaking in Geneva, WMO spokeswoman Clare Nullis said Earth is set to experience its five warmest years on record from 2015-2019. The WMO says that increasing greenhouse gas concentrations will fuel global heat and climate change.
"It's hitting the poorest and most vulnerable but it will ultimately hit everybody," Nullis said.
In Paris, near the presidential palace, about 100 students organized a street protest to urge authorities to take immediate action on climate change. The action ended without police violence.
French President Emmanuel Macron presents himself as a champion of fighting climate change, but environmental organizations say that France doesn't do enough to limit the impact of global warming.
The heat wave is caused by warm air rising across Europe from north Africa. Hot temperatures are expected to last until Sunday when a cold front will arrive on the continent.
Barry Hatton in Lisbon, Danica Kirka in London, Catherine Gaschka in Colombes, France, and Jeffrey Schaeffer in Issy-Les-Moulineaux, France contributed.