The worst-hit areas are in the south, with Gard, Ardeche and Drome seeing extreme flooding.
Heavy rains have poured down on the French department of Gard, about 150 km (90 miles) northwest of the city of Marseilles, bursting riverbanks and forcing the evacuation of children from the vacation camp of Saint-Julien-de-Peyrolas.
A German man, who was with the group, was swept away by the floodwaters in his caravan or travel trailer, which was later found "empty and in pieces" near the river.
The men, who were not named, were the president and vice-president of a charitable foundation that brought had children from Leverkusen in Germany's industrial Rhineland region to the village of Saint-Julien-de-Peyrolas, said Eric Maurel, the public prosecutor for the region.
Divers were reported to be taking part in the search for the man, although a top regional official said it was not known for certain whether the man was in his caravan at the time it was swept away.
After a hot spell, the flash flooding in the northern part of the Gard region turned the Ceze and L'Ardeche rivers into churning waterways that quickly spilled out of their banks.
'No one has suitcases.
Ten people were taken to hospitals to be treated for minor injuries, including four German children with hypothermia.
The Bagnols mayor told BFM-TV many Dutch tourists were among the 350 campers evacuated there.
France's interior ministry said in a statement that four helicopters and 400 police, security staff and firefighters have been involved in the rescue so far.
The weather in the southeast of France has improved this morning but authorities are urging people to stay vigilant as the flooding are receding.
Numerous roads in the affected area remained cut off as night fell.
Around 17,000 homes in the southwest and northeast were without power.
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As it was, David Wagner's team were unable to do enough to cause serious problems for Kepa on the young Basque 'keeper's debut. Chelsea scored the fewest goals of the top six last season and have also struggled in that department in pre-season.