Weather agency Météo France has extended its weather warnings for most of France, with 37 départements placed on orange alert - up from 14 in the morning.
In a bulletin on Wednesday afternoon, the agency extended these alerts until Friday morning.
By the late afternoon and into the early evening (see map below), temperatures will only have cooled off slightly.
And if you're hoping for a cool night then you can forget it, with the mercury set to hover above 20C throughout the evening for much of France (see map below).
The agency said that even healthy people will be at risk if they're in the areas with orange alerts, and it urged people to watch out for signs of heat stroke, especially among the sick and elderly.