MercoPress. South Atlantic News Agency

Third tidal “tsunami” keeps Venice under water; incessant rain also threatens Pisa and Florence

Venice's latest “acqua alta”, or high water, hit 150cm on Sunday, lower than Tuesday's 187cm - the highest level in half a century - but still dangerous

Venice's St Mark's Square was closed on Sunday as the historic city suffered its third major flooding in less than a week, while rain lashing the rest of Italy prompted warnings in Florence and Pisa.

Venice's latest “acqua alta”, or high water, hit 150cm on Sunday, lower than Tuesday's 187cm - the highest level in half a century - but still dangerous.

“The water has stopped rising,” tweeted mayor Luigi Brugnaro, who has estimated damage so far from the invading salt water at more than €1 billion.

“High of 150cm ... Venice is working to restart,” Brugnaro said after the sea water swamped the already devastated city where authorities have declared a state of emergency.

To the south, Tuscany president Enrico Rossi tweeted a warning of a “flood wave” on the Arno and said boards were being installed on the swollen river's banks in Pisa “as a precautionary measure”.

The Italian army tweeted photos of paratroopers helping to bolster river defenses in Pisa, with authorities monitoring the same river in Florence after heavy rain made it rise dramatically overnight.

Arno flooding devastated Renaissance jewel Florence in 1966, killing around 100 people and destroying thousands of priceless works of art. Civil protection units in Florence advised citizens “not to stand near the Arno's riverbanks”.

Firefighters tweeted footage of a hovercraft being deployed to rescue stranded citizens in southern Tuscany's Grossetano province.

The renewed threat from exceptionally high tides in Venice came after a brief respite on Saturday. Emergency workers removed temporary walkways from St Mark's Square as the water started to rise on Sunday, with only police and soldiers visible at around midday.

The top tourist site had already been shut for several hours on Friday as strong storms and winds battered the region, leaving it submerged by sea surges.

Churches, shops and homes have also been inundated in the Renaissance city, a UNESCO World Heritage site.

A massive infrastructure project called MOSE has been under way since 2003 to protect the city, but the multi-billion euro project has been plagued by cost overruns, corruption scandals and delays.

Tuesday's high waters submerged around 80 per cent of the city, officials said.

Many, including Venice's mayor, have blamed the disaster on global warming and warned that the country prone to natural disasters must wake up to the risks posed by ever more volatile seasons.