At least 20 people went missing Saturday after severe flooding in northern Italy and southern France.

One person has died and 11 others are listed as missing Saturday after severe flooding across northern Italy, officials said following torrential overnight rain.

Rivers broke their banks in Liguria and Piedmont, and falling trees caused major damage.

Local authorities had been involved in hundreds of rescue operations since late Friday, with tunnels and roads blocked due to the intensity of flooding.

In Venice, local authorities deployed the city's long-delayed flood barriers for the first time. Forecaster had warned that storms could combine with high tides to inundate the city.

Meanwhile, almost a year's average rainfall fell in less than 12 hours in the mountainous area surrounding the city of Nice, in southeastern France.

Authorities said flooding damaged houses, bridges and roads overnight in the mountainous Alpes-Maritimes region, close to the border with Italy.

Nice Mayor Christian Estrosi expressed his "emotion and sympathy" for the families of the missing. He said over 100 homes have been destroyed or severely damaged.

Firefighters said several dozen people were evacuated from their homes overnight.

French President Emmanuel Macron on Saturday expressed gratitude toward rescuers on Twitter. "Together we will get through this," he said.

France’s national weather agency, Meteo France, said that up to 500 millimeters of rain (19.7 inches) were recorded in some areas, the equivalent of almost one year of average rainfall.

Meteo 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 are expected to arrive in the area later Saturday.