0517 GMT December 14, 2018
They said a 70-year-old German man who was helping to supervise children at one of the summer camps is missing, BBC wrote.
The worst-hit areas are Gard, Ardeche and Drome. More than 400 firefighters and police — as well as four helicopters — have been deployed.
The storms which caused the floods come after a period of unusually hot weather in southern France and much of Europe.
According to UK Met Office meteorologist Marco Petagna, almost 3 inches (8 centimeters) of rain fell in a 24-hour period.
In a statement (in French), the French Interior Ministry said six departments had been placed on a flood alert, while about 17,000 homes were without power in the south-west and northeast.
In one summer camp in Saint-Julien-de-Peyrolas, in the Gard region, 119 children were evacuated.
One camper told French network BFMTV they could hear the children's cries ‘in the branches’, but were unable to reach them.
The missing German was supervising the children at the camp.
Trapped by a fast-flowing torrent, he had sought shelter inside his caravan — but the vehicle was swept away, AFP news agency reported. It was later found ‘empty and in pieces’, according to police.
Divers were called in as the search operation continued.
Regional police spokesman Jérôme Tallaron said 10 people had been taken to hospital with hypothermia and minor injuries, according to the news agency.
Harry Ollerton, from Shropshire in the UK, was camping in the Ardeche when he was woken at 05:00 on Thursday to ‘the loudest thunder and brightest flashes of lighting'.
"It didn't let up — the lightning was constant and terrifyingly close to our tent and campsite," he told the BBC.
"It passed straight over us, knocking out the power to our pitch and our phone signal suddenly went dead."
After realizing a nearby drainage ditch was overflowing, Mr. Ollerton decided it was no longer safe to stay — but even the drive to the nearest town was difficult.
"Village streets had turned into rivers and the rain was so hard that we couldn't barely see out of the window," he said.
"Some of the roads were so flooded that they were barely passable. We were lucky to make it out of the area, soaked through but unharmed, by the sound of things."
Rachel Buchanan, from Oxford in the UK, was also camping in the Ardeche when flooding hit.
"We knew a storm was imminent and couldn't believe the ferocity of last night's storm," she told the BBC.
"The level and speed of the river today was extraordinary — we woke up in about a foot of water.
"Driving in our camper van was very frightening as the road by the river was completely under water and waterfalls had appeared from nowhere crashing down the gorge."