Météo France, the country's meteorological service, issued an extra 16 Orange alert warnings in its Tuesday afternoon weather bulletin with temperatures across the country soaring.
The agency took the step of issuing an "orange alert" for a total of 40 départements in central and eastern France (see map below), up from the 26 départements that were placed on alert on Monday.
The warnings come as the heatwave hit France on Tuesday, with the agency predicting it will continue to move north east.
The agency noted that the "intense" heatwave will be the strongest since the summer of 2006, with temperatures close to the record highs for the June-July period.
An Orange warning is the second highest warning level and asks the public to be "very vigilant".
The départements on alert are all those within Bourgogne, Ile-de-France, Franche-Comté and Limousin, as well as Ain, Allier, Cher, Dordogne, Indre, Loire, Loiret, Lot, Lot-et-Garonne, Puy-de-Dôme, Aisne, Aube, Marne, Haute-Marne, Meurthe-et-Moselle, Meuse, Nord, Vosges, Cantal, Haute-Loire and Rhône.
Temperatures on Wednesday are predicted to reach 38C in the centre of the country, and the mid to high thirties in the surrounding areas.
This kind of heatwave has not been recorded at this time of year for more than 60 years, according to Météo France, which added that the temperatures were unlikely to drop below 20C at night.
(A Parisian cools off in the summer sun. Photo: AFP)
Storms in the north west on Thursday are predicted to cool down the western half of the country, but the temperatures will rise again on Friday and stay high over the weekend.
After 15,000 mostly elderly people died in a heatwave back in August 2003, the government launched an emergency response programme in which authorities can raise a three-tiered alarm system to ensure there won't be a repeat.
People are advised to drink water regularly, even when not thirsty, in order to remain hydrated. It is also wise to avoid any physical exertion and try to cool down as often as possible by taking cold showers.
The general advice is to keep the air conditioning on during the day and get the windows open at night.