The death toll from flash floods in the south-eastern French department of Var has risen to 25.
Authorities warned that more bodies could still be found as they picked through debris swept away by Tuesday's torrential rain above the Cote D'Azur.
Interior Minister Brice Hortefeux called it an "unprecedented catastrophe" for the region.
Some 2,000 rescue workers have been drafted in to search for survivors through debris and flooded houses.
A number of towns in the department of Var were affected, with hundreds of homes flooded.
Many of those who died were trapped in their cars as waters surged through streets in the worst hit area, around the town of Draguignan.
Meteo France, the national weather service, warned of further storms on Thursday.
They said up to 40cm (15.7in) of rain had fallen since Tuesday.
The floods are the worst in the region since 1827, according to meteorologists.
"We have never seen so much rain in the month of June," Patrick Galois of Meteo France told the AFP news agency.
One BBC website reader said her son was stuck for six hours on his school bus when it was cut off by the conditions.
Another, Paul Reeves, said: "In eight years of living here we have never seen rain like it, it was a wall of rain for hours."
His house lost power for 24 hours and nearby roads were impassable, he said.
"The roads are littered with rocks, boulders, debris, cars in ditches and accidents across the region."
Survivors have been recounting how a huge wave rushed toward them on the main dual carriageway, the BBC's Christian Fraser reports from the area.
Following the floods, water levels reached over 2m (6ft) in places, with helicopters air lifting people to safety, some from the roofs of their houses.
Rescue teams had to move 436 inmates from a prison in Draguignan after two floors flooded.
Rail and air services in the region were interrupted.
President Nicolas Sarkozy, who offered condolences to the families of the victims on Wednesday, plans to visit the area early next week.