At least 16 people were killed in violent storms and floods that struck the chic French Riviera overnight, and four others were missing, French authorities said on Sunday.
Up to 180 millimetres (seven inches) of rain fell in just three hours, transforming the glitzy streets of Cannes, Nice and Antibes into debris-strewn rivers.
In Cannes -- home of the famous film festival -- the torrent carried some cars out to sea, city hall said.
President Francois Hollande visited the region, expressing the "solidarity of the nation" to those affected.
"At these times, we must be fast, efficient and coordinated," he said.
Three people died when water engulfed a retirement home at Biot near Antibes, and three drowned when their car was trapped by rising waters in a small tunnel at Vallauris-Golfe-Juan.
Rescue teams at Mandelieu-la-Napoule said the water was so murky that it hampered the search for further bodies in underground car parks, where at least seven people died.
"It's apocalyptic," said mayor Henri Leroy. "There are thousands of vehicles. There could be more bodies."
In Cannes, where two people were listed as dead and two were missing, Mayor David Lisnard had tough words for some residents who, he said, were "not always disciplined".
"I'm not judging, because I don't know how I would react in that situation, but it appears we had some people that were very attached to their vehicles when they should have been saving lives," he said.
Nine people were arrested for trying to steal from shops after the storm, he added.
Hundreds of Italian pilgrims returning from the French shrine of Lourdes were trapped overnight as trains were cancelled across the region.
A special track was opened to let the pilgrims, many of them elderly and travelling with doctors, proceed at a slow pace on Sunday.
The storm "did serious damage to the railway infrastructure, tracks, crossings, electrical lines, primarily around the area of Cannes," a spokesman for French rail company SNCF told AFP.
Around 27,000 homes remained without power early Sunday, 14,000 of them in Cannes alone.
"I saw water pour in from the veranda. Within five minutes, it was up to my waist," said retired resident of Mandelieu-la-Napoule, France Oberlin, still in shock.
"I couldn't open the doors but luckily a neighbour came," she said.
Seated on a plastic chair, surrounded by debris and overturned cars, she looked despairingly at her ground-floor apartment, in which everything had been destroyed.
Communications to the region -- one of the wealthiest in France, and a magnet for visitors from around the world -- were badly hit.
Around 500 people, many of them British and Danish tourists, were stranded at Nice airport, and the A8 motorway near Antibes was flooded when a small river, the Brague, burst its banks.
A Nice-Nantes match in France's first football division was called off in the 46th minute after the pitch became a quagmire.
Nice's mayor's office estimated the city had received 10 percent of its average annual rainfall in the past two days alone.
By dawn, the worst storms had passed over the French mainland and were headed for the Italian coast, Meteo-France said.
The region's worst flood in the past 25 years was in June 2010, when 25 people were killed.
The worst national toll from flooding over this period was in January and February 1990, when 81 people were killed by violent storms in the north and west of the country.
In December 1999, 92 people in France were killed by flooding, fallen trees and other storm damage caused by hurricane-strength winds that struck northwestern Europe.