At least 25 people have been killed after torrential rains caused the worst flash flooding for two centuries in a southern region of France.

Authorities in the Var, a popular holiday region, raised the death toll to 25 from an earlier count of 19 after the floodwaters engulfed streets in torrents of mud and drove people onto the roofs of their homes. Officials warned other bodies might be found as the search continued as rescuers continued digging through mud-filled cars and wreckage for 13 people still missing. The drama was centred in the town of Draguignan about an hour west of Cannes, where 12 people died.

Floodwaters reached more than six feet in some areas as 12 inches of rain fell in as many hours, with people being rescued from rooftops by helicopter crews. Floodwaters more than six feet high transformed the roads of Draguignan, between Marseille and Monaco, into gushing brown rivers that swept away cars, trees and ripped the sides of houses in the Var department of Provence.

Torrential rains - the equivalent of six months' rainfall fell within hours - caused water levels to rise so swiftly that many people had no time to flee to higher ground and were forced to seek shelter on the roofs of their homes. Scores of cars were piled on top of each other and holiday homes and camp sites in the region were devastated.

"We opened the door of the house and the water rushed towards us like the sea. There was a great wave. We managed to swim to our neighbours," said Christine, an inhabitant of Draguignan. "It wasn't a flood, it was a catastrophe."

According to Meteo France, the national forecaster, the region has not seen such floods since 1827. Brice Hortefeux, the interior minister, described them as "an unprecedented catastrophe for the region" and said that the death toll could rise.

The floods also struck the popular tourist town of Fréjus, where more than 1,500 people were taken to safety in inflatable boats or by helicopter airlift to four shelters. Tourists were among those trapped by the floods, in particular in campsites along the Argens river. Firefighters rushed to prize people from their cars, houses or rooftops and searched for missing people.

"This morning, we woke up to find a city that was devastated, extremely battered with overturned cars floating in the streets, collapsed roads and gutted houses," said the head of the emergency operation, Corinne Orzechowski.

Emergency teams also moved 436 inmates from a flooded prison in Draguignan to nearby jails, while the rising waters also trapped a high speed train travelling from Nice to Lille with 300 passengers on board. Up to 200,000 homes suffered power cuts during the rainstorms and electricity had only been restored to around half of those by Wednesday afternoon, officials said.

All rail services between Toulon and Saint-Raphael were halted while water drained from tracks. Locals were angry that Meteo France had not given enough warning about the seriousness of the downpours in a region which regularly suffers from floods. An early warning flood system along three of the region's main rivers – long called for by locals – will only be in place next year.