France's all-time temperature record has been broken after 44.3C (111.7F) was reached in the southern town of Carpentras.
The country has been gripped by a Saharan heatwave drifting across Europe.
It is the first time in history that France has raised its heat alert to red, with Spain, Italy and Switzerland also issuing red warnings.
Temperatures have risen over the last week, with temperatures of 42C recorded in the city of Montepellier in the south.
The national weather agency has predicted temperatures could rise even more, hitting up to 45C (113F) in southern counties such as Herault, Gard, Vaucluse and Bouches-du-Rhone.
Three people have died in France so far this week in the south of the country.
One person on Monday and two on Tuesday died after diving into the sea to cool off, causing death by ‘cold shock’.
Earlier on Friday, French Prime Minister Edouard Philippe said 4,000 schools had been shut due to the extreme heat.
He tweeted: "We allowed school principles and mayors to close schools when they saw it as the right thing to do.”
In Paris, charity organisations are patrolling the streets to provide water to homeless people and local authorities have organised air-conditioned places where they can seek shelter.
On Thursday, Meteo France meteorologist France Christelle Robert said: “A heatwave of this amplitude so early in the year, in June, is exceptional.
“We should expect more intense and frequent heatwaves with climate change, because it will accentuate the extremes.”
Meanwhile, Spain is battling a large wildfire in Catalonia, the worst in the region for 20 years.