An autumn storm dubbed Alex rocked Brittany overnight, with wind gusts reaching 186 km / h at Belle-Ile-en-Mer, an island off Nantes.
Emergency services have been mobilized to clear fallen trees and downed power lines, although no deaths have been reported in the area, authorities said.
But many schools and parks have been closed, rail services have been cut off and access to the coast prohibited.
In the south-east, a road bridge was destroyed as muddy water crossed a valley near Saint-Martin-Vesubie, north of Nice, near the Italian border, Eric Ciotti, MP for AFP, told AFP. the Alpes-Maritimes region.
“The gas station was washed away, the houses were badly damaged and the stadium and cemetery were flooded” after some 235 millimeters (9 inches) of rain was poured out within hours, Ciotti said.
Beaches in Nice and other coastal towns have been closed and authorities have asked people to stay in their homes and refrain from using their cars except in emergencies.