Heavy storms hit the Languedoc-Roussillon region during the night and about 150 people had to be moved from their homes and vehicles to temporary accommodation in the Gard, Aveyron and Hérault areas.
A 60-year-old man, who was trying to rescue a woman from drowning, saw his own wife and daughter washed away by floods in a campsite at Lamalou-les-Bains in the Hérault area.
Two other people were found dead in two seperate campervans and one pedestrian was also carried off by the flood.
Police said other bodies were found on Thursday morning but they have not been identified yet.
At the Lamalou campsite the small Bitoulet river suddenly turned into a torrent and a two-metre high wave carried off caravans and campervans.
"It's a phenomenom that has never been seen here before," said a 60-year old local resident. "We had floods here 20 years ago but not to this extent".
The body of a 70-year-old woman was found Wednesday on the banks of another river, the Dourdou, in the Arnac commune in the region of Aveyron and another person is missing in the Gard.
Some 6,500 homes remain without electricity and more than 400 firefighters are working in the storm-hit areas.
More rain is expected in the region overnight.