The car, carrying a couple and their two sons aged four and one, lodged on a bridge submerged by torrential rains during the night in the Gard department of southern France.
Witnesses and rescue workers managed to help the father out but they could only watch as the car was swept away.
The father was taken to hospital in a state of shock.
Further north in the same department, another vehicle was swept away in similar circumstances, killing a man in his fifties, according to local officials.
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Meanwhile a man in his sixties died in Neffes, near Gap in southeastern France, after falling to the ground as he tried to unblock a pipe during heavy rains.
Southeastern France has seen multiple storms this autumn linked to abnormally high Mediterranean temperatures.
The first, in mid-September, left six dead.