Drivers in France are being advised to stay off the road between noon and 4pm local time and cover their rear windows because of soaring temperatures.
The guidance comes as thousands of UK motorists are in the country for summer holidays.
France is experiencing a harsher heatwave than the UK, with temperatures exceeding 40C in some areas.
Road information service Bison Fute stated that the "extreme heat" means people should avoid driving during "the hottest hours of the day (between 12pm and 4pm)".
It also urged motorists to deploy sun visors across their rear window and rear side windows to reduce the interior temperature of the vehicle.
Tony Rich, head of media for AA roadside operations, said the French authorities are concerned about road surfaces deteriorating in the heat, and people becoming stranded if they break down.
He said: "Extreme heat can lead to roads melting – they begin to soften at around 50C.
"However, even a sunny day with 20C can be enough to generate enough heat that the asphalt absorbs it and then builds up during the day, with the hottest period between noon and 5pm.
"Officials in France will also be worried about car occupants being stranded on the road.
"A short trip that might not be considered dangerous could become brutal if a vehicle ends up at the roadside and the driver and occupants have not taken adequate precautions against the heat, such as extra water, headgear, sunscreen and other protection."
