Two people died in Italy and eight were missing in France on Saturday after storms, torrential rain and flash floods battered the border area, washing away roads and houses, cutting off whole villages and triggering landslips, as hundreds of rescuers raced to find stranded survivors.
Torrential rain of up to 50 centimetres (20 inches) and high winds crashed into the border area in the latest of a string of strong storms in recent years.
Storm Alex barrelled into France's west coast on Thursday bringing powerful winds and rain across the country before moving into Italy, where regions across the north suffered an onslaught throughout Saturday.
- 'We are alive' -
"I lost everything but we are alive," said Jennyfer, 29, from Roquebilliere in France's southern Alps.
"There must be one room left in my house," she said after she returned following evacuation on Friday to survey the damage wrought by the Vesubie river.
A volunteer firefighter died in Italy's Aosta Valley and a man was killed after his car was washed away in the river Sesia, about 100 kilometres (60 miles) further east.
Italy had reported a large group of people missing after landslides hit the border area near the Col de Tende mountain pass in France.
But late Saturday the Italian civil protection agency spokeswoman Mara Anastasi said 21 people had been found and evacuated by helicopter, including two Germans and their grandchildren.
An emergency spokesman in France said that around 40 people stranded on roads by the landslides had sheltered in an old train station and then been airlifted to safety.
Dozens of firefighters were trying to reach one Italian village by train after the road was shut.
In France, the army and hundreds of rescuers were deployed to search for the missing, including using helicopters to transport aid and evacuate people where possible.
AFP journalists who reached one of the worst-hit areas in the Vesubie valley saw roads that had been washed away by the waters leaving buildings teetering above the voids.
"We have actually had houses wiped out," said Alpes-Maritimes prefect Bernard Gonzalez
Switzerland was also battered with record rainfall in some areas and powerful gusts, forcing the closure of roads and mountains.
- 'Catastrophic' -
French Prime Minister Jean Castex, who inspected the damage around the city of Nice by helicopter, said there were eight people officially designated missing.
But a great many more could not be contacted, he added.
"I do not hide from you our deep concern about the final outcome of this episode," he said, adding that the government had triggered its emergency plan for handling natural disasters.
"The situation is catastrophic in some communes," regional lawmaker Eric Ciotti told AFP.
Authorities in the Alpes-Maritimes region had been placed on alert Friday and around 12,000 people in three valleys to the north of Nice were without power early Saturday afternoon.
"We are thunderstruck," said Serge Franco, a resident of Roquebilliere, some 50 kilometres (30 miles) north of Nice, as rescue helicopters hovered overhead.
"We saw the (river) Vesubie burst its banks -- everything was swept away, including part of the old iron bridge," he told AFP.
"My house is habitable but half of my land has been swept away," said another resident, Guillaume Andre. Evacuated overnight, he had returned to see the devastation after daybreak.
In Roquebilliere, the floodwaters swept away two elderly people with their house.
The head of Italy's Piedmont region said the storm was the most serious in those parts since a flood killed 70 people in 1994.
The mayor of the northern Italian city of Ventimiglia, Gaetano Scullino, meanwhile said "a disaster of this kind has not happened since 1958".