Venice was hit by the highest tide in more than 50 years late on Tuesday, with tourists wading through flooded streets to seek shelter as a fierce wind whipped up waves in St Mark's Square.

The exceptionally intense "acqua alta," or high waters, peaked at 1.87 metres (six feet) as the flood alarm sounded across Italy's iconic city of canals, the tide monitoring centre said.

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

The vestibule of the basilica was inundated with water, and authorities planned to watch the building overnight.

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.

Most worryingly, Campostrini said, three of those five episodes occurred in the last 20 years, most recently in 2018.