 People have been urged to stay in the shade and drink plenty of water |
French officials said 40 of the victims were over 75 years old.
There are fears that the death toll could rise, even though the high temperatures, above 35C (95F) in some places, dropped after overnight storms.
The heat has brought back memories of 2003, when some 15,000 people died in France, most of them elderly.
"The number we have established up to yesterday [Wednesday] is 64 deaths," Gilles Brucker, director of the French Institute of Health Surveillance told reporters.
Mr Brucker said the deaths were "directly or indirectly caused by this heatwave".
Of the total, 40 people were over 75 years of age, he said.
Overnight thunderstorms brought cooler weather across much of France, but Mr Brucker warned that "the consequences of a heatwave can make themselves felt for 24 or 48 hours".
Meanwhile, Germany, Spain and Italy are also sweltering, with temperatures reaching 37C (98.6F) in some places.
The heatwave has been accompanied by increased pollution and drought.
In the Swiss city of Zurich, zookeepers said they had been serving the animals ice creams made of berries, meat and bones to cool them down.
