Two people have reportedly died as Venice was hit by its highest tide in more than 50 years, leaving much of the Italian city under water.
The flooding was the second highest in the city's history, and the mayor blamed climate change. Officials said the tide peaked at 187cm (6.14ft) at 10.50pm on Tuesday, just short of the 194cm seen in 1966.
The high water submerged the city's historic squares and alleyways, including some of the favourite tourist spots such as St Mark's Square.
A man in his 70s died on the barrier island of Pellestrina after being electrocuted, and another person died on the same island, though the cause was unknown, the Italian news agency ANSA and other reports said.
Saint Mark's Basilica, parts of which date to the 11th century, was flooded, with an official even pointing to a risk of collapse during the worst of the flooding.
"We were on the verge of the apocalypse", said Pierpaolo Campostrini, a member of St Mark's Council.
"The water could have imperilled the columns that hold up the basilica," he was quoted as saying by Italian newspaper Corriere della Sera.
Visitors were forced to make their way along temporary platforms above the water, while others donned wet weather gear and sloshed through the floods.
Cafes, stores and other businesses were inundated by high water and nursery schools were closed as a precaution.
Saint Mark's Square had more than a metre (3.3ft) of water and Saint Mark's Basilica was flooded for only the sixth time in 1,200 years - four of those being in the last two decades.
The extent of damage to the historical church is not clear but when it last flooded in 2018, its administrator said it had aged 20 years in a single day.
Mayor Luigi Brugnaro called for the state of emergency to be declared, and the Italian prime minister, Giuseppe Conte, said he would visit the city to assess the damage first-hand.
Mr Brugnaro said: "The situation is dramatic. We ask the government to help us. The cost will be high.
"This is the result of climate change. A high tide of 187 cm is going to leave an indelible wound."
The high water is known locally as "acqua alta" but even low levels take their toll - eroding the foundations of buildings in the lagoon city.
It comes after authorities announced that access to La Pelosa Beach in northwest Sardinia will be limited to 1,500 people per day, with entrants having to pay a fee.
:: A New Climate is a series of special podcasts from the Sky News Daily. Listen on Apple Podcasts , Google Podcasts , Spotify , Spreaker
The fee will be used to maintain and monitor the beach, according to Stintino mayor Antonio Diana, who said the white sand paradise had been suffering under the strain of its popularity.
Beachgoers breaking the rules will be fined up to €500.