An exceptionally high tide has inundated Venice, putting three-quarters of the famous Italian city under water as large swathes of the country experience deadly flooding and heavy winds.

Key points: Six people have died across the country in wild weather

Six people have died across the country in wild weather Water levels in Venice rose by more than 1.5 metres

Water levels in Venice rose by more than 1.5 metres Venice often floods when high winds push in water from the lagoon

Six people died in four separate incidents in Naples, Lazio and Liguria, after gale-force winds brought down trees.

Tourists and residents of Venice donned high boots to navigate the city's streets, after strong winds raised the water level by more than 1.5 metres before receding.

The water exceeded the raised walkways normally put out in flooded areas in Venice, forcing their removal.

Transport officials closed the water bus system except to outlying islands because of the emergency.

Heavy rains and high winds have flooded many parts of Italy. ( ANSA via AP: Andrea Merola )

Venice frequently floods when high winds push in water from the lagoon, but Monday's levels were exceptional, with the peak water level the highest since December 2008, according to local statistics.

Venice's Mayor Luigi Brugnaro said a series of underwater barriers currently being built in the lagoon would have prevented the inundation.

He said that the project was not completed due to cost overruns and corruption scandals.

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Mr Brugnaro said he had asked to talk with Prime Minister Giuseppe Conte to underline the urgency of the project, which would raise barriers when the tide reaches 109 centimetres.

Residents and businesses typically reinforce their doors with metal or wooden panels to prevent water from entering the bottom floors, but photos on social media showed shop owners using water pumps to try and protect their wares.

Much of Italy is still under alert for flooding from heavy rains, a problem exacerbated by a lack of maintenance of the country's many river beds.

A woman uses a bucket to remove water from a shop in Venice. ( ANSA via AP: Andrea Merola )

High winds toppled trees that killed passers-by in four incidents in Naples, Lazio and Liguria. Two of the deaths occurred in the Lazio Region municipality of Castrocielo, when a falling tree struck a car.

Officials closed major tourist attractions early in Rome, including the Colosseum and Roman Forum, because of heavy rains.

The Interior Ministry urged officials in storm-affected regions to consider closing schools and offices for a second day on Tuesday.

AP/Reuters