Venice was hit by the highest tide in more than 50 years yesterday, with tourists wading through flooded streets to seek shelter as a fierce wind whipped up waves in Piazza San Marco, also known as St Mark's Square.

The exceptionally intense "acqua alta", or high waters, peaked at 1.87 metres as the flood alarm sounded across the Italian city of canals, the tide monitoring centre said.

"We're currently facing an exceptionally high tide. Everyone has been mobilised to cope with the emergency," Venice's mayor Luigi Brugnaro tweeted.

Only once since records began in 1923 has the water crept even higher, reaching 1.94 metres in 1966.

Tables and chairs set out for visitors bobbed along alleyways in the dark, as locals and tourists alike waved aloft inside-out umbrellas, the water slopping over the top of even the highest waders and wellies.

Water taxis attempting to drop people off at the glamorous and historic hotels along the Grand Canal discovered the gangways had been washed away, and had to help passengers clamber through windows.

"It will be a long night," Brugnaro tweeted, saying that as the water level began to drop again "the fears of a few hours ago are now being replaced by an assessment of the damage done". The exceptional flood, which he blamed on climate change, was "a wound that will leave a permanent mark".

At the sumptuous Gritti Palace, which has played host to royals and celebrities over the decades, including Ernest Hemingway, Elizabeth Taylor and Richard Burton, the decadent bar was largely underwater. Rich tapestries were piled onto tables, while the waters lapped around velvet sofas and leather-bound books.

A couple of French tourists caught out said they had "effectively swum" after some of the wooden platforms placed around the city in areas prone to flooding overturned.

Since 2003, a massive infrastructure project has been under way to protect the city, but it has been plagued by cost overruns, scandals and delays.

St Mark's Square is particularly affected by the high tides, as it is located in one of the lowest parts of the city.

Last night, the vestibule of the basilica was inundated with water. Pierpaolo Campostrini, a member of St. Mark's council, said the scale of the flooding on Tuesday had only been seen five times in the long history of the basilica, where construction began in 828 and which was rebuilt after a fire in 1063.