Flood-hit Venice was bracing for another exceptional high tide Friday, as Italy declared a state of emergency for the UNESCO city where perilous deluges have caused millions of euros worth of damage.

Churches, shops and homes in the city of canals have been inundated by unusually intense "acqua alta", or high waters, which on Tuesday hit their highest level in half a century.

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Much of Venice was left under water this week after the highest tide in 50 years ripped through the historic Italian city Photo: AFP / Filippo MONTEFORTE Filippo Monteforte/AFP

The crisis, driven by bad weather, has prompted the government to release 20 million euros ($22 million) in funds to tackle the devastation.

The water was expected to reach 1.5 metres (5 feet) mid-morning on Friday as strong storms and winds batter the region -- lower than Tuesday's peak but still dangerous, local officials said.

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The high waters peaked at 1.87 metres (six feet) on Tuesday Photo: AFP / Marco Bertorello Marco Bertorello/AFP

Undeterred, tourists have been larking around in the flooded St Mark's Square in the sunshine during breaks from the rain, snapping selfies in neon plastic boots.

Prime Minister Giuseppe Conte, who has called the flooding "a blow to the heart of our country", said late Thursday that a state of emergency had been approved.

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Officials erected a footbridge across a flooded street after the tide hit Photo: AFP / Marco Bertorello Marco Bertorello/AFP

Earlier that day he met Venice's mayor and emergency services before jumping in a speed boat to visit businesses and locals affected by the tide.

Residents whose houses had been hit would immediately get up to 5,000 euros in government aid, while restaurant and shop owners could receive up to 20,000 euros and apply for more later, he said.

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An artwork by Banksy portraying a migrant child wearing a lifejacket and holding a neon pink flare remained just above water Photo: AFP / Marco Bertorello Marco Bertorello/AFP

Several museums remained closed to the public on Thursday.

As authorities assessed the extent of the damage to Venice's cultural treasures, such as St Mark's Basilica where water invaded the crypt, locals were defiant.

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Chart showing maximum documented high tide levels in Italy's Venice Photo: AFP / Gal ROMA Gal Roma/AFP

Many stopped for their usual coffees at flooded bars, drinking espresso while standing in several inches of water.

Austrian tourist Cornelia Litschauer, 28, said she felt mixed emotions seeing Venice's famous square half-submerged.

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Local business owners remained defiant in the face of the flooding Photo: AFP / Filippo MONTEFORTE Filippo Monteforte/AFP

"For the tourists it's amazing, it's something to see. But for the people who live here it's a real problem," Litschauer said, cradling her white Chihuahua Pablo.

"It's strange. Tourists are taking pictures but the city is suffering."

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The flooding caused millions of euros worth of damage to the UNESCO city, according to officials Photo: AFP / Filippo MONTEFORTE Filippo Monteforte/AFP
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Floodwaters continue to cover Venice's San Marco Square after Tuesday's exceptional high tide Photo: AFPTV / Sonia LOGRE Sonia Logre/AFPTV

The Locanda Al Leon hotel said its bookings had suffered from the international media coverage of the flood, with some guests cancelling their rooms after seeing images of Venice underwater.

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

"This (trip) was planned a long time ago so we couldn't change it," groom Jay Wong, 34, said.

"Actually this is a good experience. It's an adventure."

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

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

Former prime minister Silvio Berlusconi arrived for a private tour of the damage sustained to the basilica, while rival leader of the Italian right Matteo Salvini was due to drop by for the same on Friday.

French tourist Manon Gaudre, 22, said seeing Venice submerged was a "unique experience".

"The damage it's causing to monuments and the people is worrying," she said, wondering if climate change was to blame.

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

"We need to be resilient and adapt. We need a policy that looks at the climate through completely different eyes," Environment Minister Sergio Costa said Thursday.

Mayor Luigi Brugnaro has estimated the damage to Venice at hundreds of millions of euros.

The Serenissima, as the floating city is called, is home to a mere 50,000 residents but receives 36 million global visitors each year.

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

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