Dozens of people were evacuated from their homes Friday after the equivalent of a month's worth of rain fell in six hours, flooding streets and swelling waterways in Tuscany, the region where Florence is located.

"The important flood peak of the Arno passed along the entire length without any critical issues," Tuscany's president, Eugenio Giani, wrote on social media Saturday.

Giani said the region's floodgate and expansion basins were "decisive" in lowering the threat to the famous Renaissance city and surrounding areas, including Pisa.

"In these difficult hours, the hydraulic safety system of the region has made the difference despite the intense and persistent rainfall," he said.

On Saturday morning, the level of the Arno was at 3.87 metres (12.7 feet) and slowly receding, said Florence mayor Sara Funaro, who added that the levels of all tributaries had fallen below warning levels.

On Friday evening, the river had surpassed four metres.

A red weather alert remains in effect Saturday till 1400 GMT, with parks, cemeteries, markets, museums and libraries closed.

The Arno, which runs through Florence and Pisa, is prone to flooding in spring and fall.

A floodgate located between Pisa and Florence, which authorities ordered opened Friday afternoon, "literally knocked down the Arno flood wave that was rising," Giani said.

Construction of the floodgate began after a devastating flood in 1949. But it was not completed in time to help avert another massive flood in 1996 which killed over 100 people and destroyed or damaged countless works of art.

Approximately 500 firefighters worked over the past 24 hours to carry out 430 interventions in the provinces of Florence, Prato, Pisa and Livorno, including rescues, due to flooding, landslides, the fire service said.

Authorities were still responding to "critical issues" in certain towns outside Florence, he said.

Friday's red weather alert caused Florence's world-famous Uffizi Galleries to close early, along with the Duomo cathedral.

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