Regional authorities in the French capital Paris have warned residents to be vigilant, with temperatures soaring to 36C.
In a tweet, the Ile-de-France prefecture also asked residents to moderate their water consumption amid a “major dry spell”.
Elsewhere in France, some 27 departments have now been placed on “orange alert”, with a heatwave spreading mainly to the east of mainland France.
Temperatures are set to hit up to 40C in some places in the south.
The heat will reach its peak on Wednesday, and begin to decline on Thursday.
This heatwave should be shorter than that of July, according to the French weather agency.