According to the interior ministry, a total of 1,600 people, majority campers, were evacuated as a precaution in Gard and the nearby Ardeche and Drome regions.
In one summer camp in Saint-Julien-de-Peyrolas, 119 children were evacuated.
The mayor of Bagnols, Jean-Yves Chapelet, told BFM-TV many Dutch tourists were among the 350 campers evacuated there.
District official Thierry Dousset said it was not certain whether the 70-year-old had been in his van at the time.
Four German children suffering from hypothermia were taken to hospital in Bagnols-sur-Ceze, around 65 miles from Montpellier.
The bad weather caused large power cuts, and a man who was working in a summer camp was reported missing.
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After weeks of dry and hot conditions, recent torrential downpours quickly swelled the Ceze and L'Ardeche rivers in the Gard region.
A man is missing and 1,600 people have been rescued after severe flooding hit parts of southern France popular with British holidaymakers overnight.
Hundreds of tourists have been whisked to safety in helicopters after flash floods submerged campsites in southern France.
"No one has suitcases". We just have what we're wearing, ' Rita Mauersberger, a visitor from Germany who was among the campers taking shelter in a local hall in Saint-Julien-de-Peyrolas, told France Info radio.
Tents have been destroyed and roads overwhelmed with water after nearly three inches of rain fell in under 24 hours, causing rivers to overflow at a rapid rate.
About 400 firefighters and policemen, backed by four helicopters, helped in the evacuations and performed rescue operations, the French interior minister said.