A 70-year-old German man helping to supervise children at a summer camp at Saint-Julien-de-Peyrolas in Gard was feared to have been swept away by floodwaters along with his van yesterday.
Rescuers believe the man sought shelter in his camper when fast-flowing water burst the banks of the nearby L'Ardeche River, but the vehicle was swept away. Divers and a helicopter have been deployed to search for the missing man, Souliman said.
A top regional official, Thierry Dousset, told French news channel BFM TV that the some 750 people evacuated came from five campsites. A group of 136 children and youths from the German city of Leverkusen were reported safe.
Four German citizens were also taken to hospital for hypothermia.More news: Bowing to Israeli bullying, BBC changes Gaza killings headline
The worst hit areas are Gard, Ardèche and Drôme, which are all popular holiday sites.
He was the only person unaccounted for after a rescue operation at three campsites in the area, where a heatwave ended abruptly this week in storms that caused flash flooding.
Videos posted on social media showed flood water rushing through populated areas.
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More than 400 firefighters and gendarmes, many sent in from other regions, helped in the evacuations, using helicopters to spot camp sites and to perform rescues.
UK Met Office meteorologist Marco Petagna said almost 3 inches of rain fell over the area in just 24 hours.
Hardest hit was the Gard region, where 119 children, many of them from Germany, were evacuated from their campsite at Saint-Julien-de-Peyrolas, Interior Minister Gerard Collomb said in a statement.
Pictures showed rescuers wading through flooded campsites with damage to tents, caravans and bicycles.More news: Brad Pitt says he has given Angelina Jolie millions since split
The French weather service has issued orange and yellow alerts for parts of south-east France that will remain in place until 4pm on Friday.