At least three people were killed in France and a landslide collapsed a stretch of elevated road in Italy, leaving cars perched perilously on a precipice as heavy rains pounded the region over the weekend.
The rain trapped travellers, downed trees and unleashed mudslides, and triggered floods in parts of both countries.
A 100ft section of road along a viaduct near the flooded Italian coastal city of Savona collapsed on Sunday.
In an aerial video taken by firefighters, cars and one lorry could be seen stopped perilously close to the point where the raised part of the A6 road plunged on to a wooded area of the Liguria region.
A man from one of the cars closest to the precipice stood outside his vehicle, holding up his arms toward other traffic to make sure drivers stopped.
Liguria governor Giovanni Toti said a landslide caused the collapse in a muddy, hilly area.
Firefighters were using dogs to sniff out any possible victims in 6.5ft debris of mud, Mr Toti said.
It was not known if any vehicles might have plunged off the road, which is supported by pillars at that point.
The road gave way about a mile outside Savona which links the city to Turin.
The collapse was reminiscent of the 2018 bridge tragedy in Genoa during a rainstorm that killed 43 people, when trucks and cars plunged into a dry riverbed below.
Elsewhere in northern Italy, a woman was found dead after the surging Bomida river swept away her car.
Flooding in Turin, north-west Italy, prompted cancellation of a marathon. In France, the Nice airport was briefly closed Saturday.
Rivers leading from the Alps to the French Riviera broke their banks, and sirens rang out in resort towns. Images on French media showed cars peeking above inundated streets and waves slamming on to roadsides.
A rescue boat sank while taking three people to shore near the French town of Muy, and one of them died, the Var regional administration said.
Another person was found dead in a car in the town of Cabasse.
French authorities are searching for two people missing in the floods, Nice mayor Christian Estrosi said Sunday.
Rain-swollen rivers and flooded streets plagued Italy, where it has been raining, sometimes heavily, in much of the country nearly every day for about two weeks.
In Turin, the Po River overran its banks and flooded the medieval quarter and a popular riverside strolling area known as the Murazzi.
Some 150 people were evacuated from their homes in Liguria, Italy’s hilly northwest coastal region.
The region struggled with mudslides that blocked several roads, isolating hamlets.
In Genoa, the region’s principal city, the charming neighbuorhood of Boccadasse, a former fishing village with pastel-painted houses, was flooded after the sea rushed over retaining walls and on to the seaside road.
Venice was partially flooded, but the high tide’s level of nearly 4.3ft in late morning was not unusual for the lagoon city accustomed to the phenomenon of “acqua alta’’ (high water).
That level was nearly two feet lower than the exceptionally high wind-driven tide that devastated the art-rich tourist destination earlier this month.
In Puglia, the ‘’heel’’ of the Italian peninsula, authorities in the Baroque city of Lecce ordered as a precaution on Sunday the closing of parks and cemeteries for fear that storm-battered trees might crash on to visitors, the Italian news agency Ansa said.
In addition to the two dead in France, rescuers are searching for at least four others, French Interior Minister Christophe Castaner said after visiting the area Sunday. He said more than 1,600 people have been evacuated.
French national weather service Meteo France said the area absorbed the equivalent of two months of average rainfall in 24 hours.