Saturday was the hottest day in France since the 2003 heatwave, in which several thousand people died, according to Météo-France weather-watcher François Jobard.
Records were broken overnight in southern towns such as Cap Béar, where temperatures did not go below 29.4°C and Toreilles, which was never cooler than 28.9°C.
And, after a slight fall Sunday, temperatures were expected to climb even higher, reaching a peak in the south on Monday and on Tuesday further north.
After the heat from the Sahara that has affected the country this weekend, a mass of air from the Atlantic should cool it down from Wednesday onwards.
Cities must adapt
Health Minister Agnès Buzyn, who put off leaving on holiday because of the extreme weather, visited emergency services in Paris on Sunday before holding a press conference.
Only 18 of France's hospital emergency units were "under tension", she reported, a "relatively low" number that indicates that "our society is beginning to adapt to heatwaves".
But she stressed the need for vigilance, particularly against the danger of drowning or heat-related illnesses for children, particularly babies.
"With climate change, we believe that there will be more such episodes," she said. "They are likely to be more intense and so it will necessary to adapt our habitat, the planning of our towns, which are very mineral and encourage heat retention, especially at night."
With ozone pollution rising, Paris city council announced that heavy-polluting vehicles would be banned from the streets on Monday, although the police would be indulgent to people leaving for their holidays.