Authorities were looking for 17 missing people in the neighboring Piedmont region, mostly people traveling by car in the high mountain pass of Col de Tende between France and Italy, according to civil protection authorities.
Among them, two Germans driving with their grandchildren aged 11 and 6, and a pair of brothers returning from France.
A man was reportedly swept away by a swollen river after getting out of his car in Verceil province.
Relentless rains have reached levels not seen since 1958 in the Piedmont region of northern Italy, where up to 630 millimeters of rain fell in 24 hours, according to the Italian Civil Protection Agency.
Two brothers were swept away by flood waters while guarding animals near the French border. One brother managed to hang on to a tree and was saved, while the authorities searched the French side for the other brother.
Eleven campers were rescued in the province of Vercelli, where floodwaters peaked in 20 years. And the Alpine rescue teams evacuated on foot seven people who were in houses cut off by the floods in Terme di Valdieri; some had to be transported on stretchers due to muddy conditions and litter build-up.
Across the border in south-eastern France, nearly a year of average precipitation fell in less than 12 hours in the mountainous area surrounding the city of Nice.
Local firefighters said at least eight people were missing, including two firefighters whose vehicles were washed away when the road collapsed during a rescue operation.
The mayor of Nice, Christian Estrosi, expressed his “emotion and sympathy” for the families. He said more than 100 houses have been destroyed or badly damaged.
Firefighters said several dozen people were evacuated from their homes overnight.
French President Emmanuel Macron expressed his gratitude to the rescuers on Twitter on Saturday. “Together we will overcome this,” he said.
France’s national meteorological agency Météo France said up to 500 millimeters of rain had been recorded in some areas, equivalent to nearly a year of average rainfall.
Météo France had issued a danger alert on Friday and all schools in the region had been closed. Local authorities urged people to stay at home.
French Prime Minister Jean Castex and Interior Minister Gerald Darmanin arrived in the region later on Saturday.