The storm, dubbed Alex, ravaged several villages around the city of Nice on the French Riviera. Nice Mayor Christian Estrosi called it the worst flooding disaster in the area for more than a century after flying over the worst-hit area by helicopter.
“The roads and about 100 houses were swept away or partially destroyed,” he told French news channel BFM.
At least eight people were missing in France, authorities said. These included two firemen whose vehicle was carried away by a swollen river, according to local witnesses cited by several French media.
In Italy, at least one person died and up to 11 people were missing, local authorities said.
A fireman was killed by a falling tree in the Valle d’Aosta region, while three people traveling in a van were swept away by flood waters in Val Roya on the border with France.
Six German trekkers were among the missing after failing to return from a trip in the mountains in the province of Cuneo.
Officials in the Piedmont region reported a record 630 mm (24.8 inches) of rain in just 24 hours in Sambughetto, close to the border with Switzerland. The Piedmont regional chief Alberto Cirio called on the government to declare a state of emergency.
Television images shot in Italy showed several roads and bridges in the northwest of the country had been swept away by flood water and numerous rivers were reported to have burst their banks.
Eric Ciotti, a member of French parliament who is from one of the worst affected villages in the area, Saint-Martin-Vésubie, said several villages were cut off as they are located in steep-sided valleys of the mountainous region.
Meteo France said that rains of 450 mm (17.7 inches) of rain were registered over 24 hours in some areas – the equivalent of close to four months of rain at this time of the year.
There was more rainfall than on Oct. 3 2015, when floods caused the death of 20 people in and around the French Riviera city of Cannes, Jérémy Crunchant, the director of civil protection, told France Info.
Venice, a long-delayed flood barrier system successfully protected the lagoon city from a high tide for the first time on Saturday, bringing big relief following years of repeated inundations.