VENICE has declared a state of emergency after a 1.8-metre flood caused hundreds of millions of pounds worth of damage to the tourist hot spot and killed at least two people.
Shocking images show the historic St Mark's Basilica under water - as the regional governor described a scene of "apocalyptic devastation" following the worst floods in 50 years.
Luca Zaia, governor of the Veneto region, said: "There's apocalyptic devastation.
"Venice is on its knees... the art, the basilica, the shops and the homes, a disaster.. The city is bracing itself for the next high tide."
Saint Mark's Square was submerged by more than one metre of water, while the adjacent Saint Mark's Basilica was flooded for only the sixth time in 1,200 years - sparking fears for millions of pounds worth of priceless art.
The floods have also brought misery to tourists and local residents - stranding boats, battering shops and hotels and and leaving many of the city's squares and alleyways deep underwater.
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The city's Mayor Luigi Brugnaro blamed climate change for the "dramatic situation" after one man died as a direct result of the flooding.
He claimed the basilica had suffered "grave damage", but no details were available on the state of its world-famous Byzantine interior.
The building's administrator said it aged 20 years in a single day when it flooded last year.
The victim, a local man from Pellestrina, was killed after being struck by lightning while using an electric water pump.
The body of another man was reportedly found when concerned relatives entered his home.
Is it safe to travel to Venice?
An estimated 85 per cent of the city is underwater, sparking concerns over damage to ancient mosaics and artworks.
One of two people reportedly killed in the floods, a local man from Pellestrina, died after being struck by lightning while using an electric water pump.
Venice mayor Luigi Brugnaro has called for the city to be declared a disaster zone, warning "the cost will be high."
But the city's businesses are also very used to dealing with flooding and while many of the tourist attractions, cafes and restaurants are closed, some have remained open, including the Ducal Palace and the Museo Archeologico Nazionale di Venezia.
The city has also installed raised walkways in certain parts to enable pedestrians to get around.
Night-time footage showed a torrent of water whipped up by high winds raging through the city centre.
Tables and chairs bobbled along alleyways as locals waded to their hotels.
Transport officials closed the water bus system - except to surrounding islands - because of the emergency.
One posh hotel was forced to stack priceless tapestries on tables after a "waterfall" swamped the bar.
A museum of modern art was evacuated after the floodwater sparked an electrical fire.
And two French tourists were forced to SWIM back to their hotel after a makeshift bridge overturned.
Only once since records began in 1923 has the tide been higher, reaching 1.94m (6ft 5ins) in 1966.
Dramatic photos show taxi boats and gondolas grounded on walkways flanking canals.
An estimated 85 per cent of the city is underwater, sparking concerns over damage to ancient mosaics and artworks.
Why is Venice so prone to flooding?
Venice experiences a phenomenon 'acqua alta' or 'high water' due to exceptional tide peaks in the Adriatric Sea.
The tidal peaks reach their maximum level in the Venetian Lagoon, which runs around and through the city, causing flooding in the region.
The causes of the tidal peaks are down to a number of factors, including the movement and phase of the moon, wind strengths and direction as well as rain level and rising sea-levels.
Exceptionally high tides in Venice occurs once every four years, on average.
However minor flooding in the city happens around four times a year and usually within the winter months.
High water can sometimes last only for a few hours but it is dependent on which part of the island is hit by floodwaters.
Natalie and Watine Olivier arrived in Venice as the high tide struck. Their plans to visit the Venice Biennale have been dashed.
Watine Olivier, 68, a surgeon in Lille, France, said: "We walked back to our hotel and the water rose before our eyes. It rose about 50cm in ten minutes."
He added: "There is no difference between the grand canal and the street."
Petra Vencelidesova, 31, a film set designer visiting from Prague, said the flooding felt "like an apocalypse".
Caught in St Marks Square at the time of the rising tide, she described the chaos.
"All the ships were flooded, the shop fronts were inundated with water from broken windows. I saw people waist-high in the water taking photos.
"I feel sorry for the people who live and work here ... the shopkeepers were scooping water in buckets and throwing it out their windows. It was crazy. It felt like a movie."