France placed 35 departments under the highest red heat wave alert on Sunday, while 45 others remained under orange alert, as authorities warned that temperatures could approach record levels in the coming days, according to RTL.
National weather agency Meteo-France said temperatures could locally reach 41C (105.8F) on Sunday and warned that Monday is expected to be even hotter.
The agency said the national average temperature could match the highest daily level ever recorded in France, regardless of season.
Maximum temperatures are forecast to range between 40C (104F) and 42C (107.6F) in areas under red alert.
Meteo-France said the heat wave is expected to persist through much of next week, with exceptionally high daytime and nighttime temperatures likely to continue until at least Thursday.
It also placed four departments under a high forest fire risk warning on Sunday and said the number would rise to 11 on Monday as hot and dry conditions persist across parts of the country.
Authorities have not ruled out extending the red alert to additional departments on Monday.
The extreme weather has prompted special measures ahead of France's annual Music Festival (Fete de la Musique) on Sunday evening.
The government announced a ban on public alcohol consumption in departments under red alert, while Paris police deployed additional river patrols to prevent drownings and prohibited undeclared gatherings along parts of the Seine river.
According to police authorities, 4,800 police officers and gendarmes, along with 2,500 firefighters, were mobilized in Paris and its surrounding region for the event.
The heat wave has also been linked to several drowning deaths.
A 17-year-old boy died after being swept away by a current in the Dordogne River in southwestern France on Saturday evening, emergency services said.
Separately, a 16-year-old boy drowned on a beach in Dunkirk in northern France on Saturday, while two other teenagers died in eastern France on Friday after drowning in the Doubs River.
French railway operator SNCF said it had activated emergency measures to maintain services despite the extreme temperatures.
"We are fully mobilized to face these events and ensure traffic remains as normal as possible under these extreme conditions," SNCF chief executive Jean Castex said.
French Transport Minister Philippe Tabarot told BFMTV that the country's railway network was "aging" and called for additional investment to accelerate infrastructure renewal.
He said authorities had taken measures to prepare for the heat wave, but warned that its intensity and unusually early arrival were forcing officials to make decisions aimed at preventing public services, particularly the healthcare system, from becoming overwhelmed.
