Ferocious storms and torrential rains that lashed France, Switzerland and Italy this weekend have left seven people dead, local authorities said on Sunday.

Three people in their 70s and 80s died in France's northeastern Aube region on Saturday when a tree crushed the car they were travelling in during fierce winds, the local authority said.

A fourth passenger was in critical care, it added.

In neighbouring Switzerland, four people have died and another is missing, according to local police.

Three were killed after torrential rains triggered a landslide in the southeast, police in the Italian-speaking canton of Ticino said.

A man was also found dead in a hotel in Saas-Grun in the southwest canton of Valais, police said, adding that he was probably taken by surprise by a sudden rapid rise in floodwater.

Another man is also missing in Valais, police said.

The civil security services said "several hundred" people were evacuated in Valais and roads closed after the Rhone and its tributaries overflowed in different locations.

Emergency services were assessing the best way to evacuate 300 people who had arrived for a football tournament in Peccia, while almost 70 more were being evacuated from a holiday camp in the village of Mogno.

The poor weather was making rescue work particularly difficult, police had said earlier, with several valleys inaccessible and cut off from the electricity network.

The federal alert system also said part of the canton was without drinking water.

Extreme rainfall also struck southeastern Switzerland last weekend, leaving one dead and causing major damage.

In northern Italy's Aosta Valley, internet users shared images of spectacular floods and swollen rivers rushing down mountain slopes. (AFP)