Venice braced itself for more rising waters on Thursday as Italy's government prepared to take emergency measures for the canal city struck by an exceptional tide this week.

Venetians awoke to sirens indicating that the high waters were expected to exceed 130 centimetres (50 inches), enough to bring the salty dirty water back again into the UNESCO city's historic centre.

On Tuesday, the highest tide in 50 years ripped through the historic Italian city, peaking at 1.87 metres (six feet).

As authorities on Thursday prepared to assess the extent of the damage to Venice's cultural treasures, such as St Mark's Basilica where water had invaded the crypt, locals remained defiant.

"It's my living, what can I do?" Stefano Gabbanoto, 54, replied when asked why he was opening his newspaper kiosk knowing he would have to close up soon.

People take pictures at the flooded St. Mark's Square in Venice, Italy. Reuters

He said he would continue to sell the colourful plastic high boots stacked in bins around the kiosk even once it was shut.

A flooded St.Mark's Square is pictured during a period of seasonal high water in Venice, Italy on Tuesday.

Under the arches of the Ducal Palace, a couple from Hong Kong posed for photos and video in the chilly morning sun.

"This was planned a long time ago so we couldn't change it," groom Jay Wong, 34, said. His bride, Sabrina Lee, "looks cold," he admitted.

"Actually this is a good experience," Wong said. "It's an aventure."

Workers cross a bridge during a period of seasonal high water in Venice. Reuters

Prime Minister Giuseppe Conte was set to meet Venice's mayor and emergency responders before visiting businesses affected by the tide.

On Wednesday, Conte called the flooding "a blow to the heart of our country", with the government expected to declare a state of emergency over the natural disaster.

People walk on a catwalk in the flooded St.Mark's Square during a period of seasonal high water in Venice on Tuesday.

Video on social media showed deep waters flowing like a river along one of Venice’s main thoroughfares, while another showed large waves hammering boats moored alongside the Doge’s Palace and surging over the stone sidewalks.

“A high tide of 187 cm is going to leave an indelible wound,” Brugnaro said.

People walk in the flooded St. Mark's Square in Venice. Reuters

Much of Italy has been pummelled by torrential rains in recent days, with wide spreading flooding, especially in the southern heel and toe of the country.

In Matera, this year’s European Capital of Culture, rain water cascaded through the streets and inundated the city’s famous cave-dwelling district.

Further bad weather is forecast for the coming days.

Reuters