Heavy rains have caused flash floods in south-eastern France and north-western Italy, killing at least nine people on both sides of the border.
Storm Alex has destroyed dozens of houses and washed away roads in a mountainous border region near Nice.
Coastal areas on the French Riviera were devastated, with long stretches of beaches littered with storm debris.
Meanwhile, rescue workers stepped up their search efforts amid fears that up to 20 people were missing.
On Monday, French officials said three more bodies had been found in villages north of Nice, bringing the death toll in the country to four. At least three people have been killed in Italy, according to BBC reports.