VENICE, Italy (AFP) – Venice suffered its worst flooding in 22 years on Monday as water in the Renaissance city stood more than 1.5 metres (five feet) deep before beginning to recede.
A change in the direction of the wind helped the "acqua alta" (high water) water start backing down from a high of 1.56 metres (5 feet, 2 inches), the tide monitoring centre said.
Authorities had warned that the sea lapping at the lagoon city threatened to rise to 1.60 metres, a 30-year high mark, and warned residents and tourists to stay indoors.
"It's an exceptional 'acqua alta,' and unless you absolutely have to, don't go out," Venice mayor Massimo Cacciari said in a statement.
Nearly all the streets of the city, including the central tourist district, were already under water by mid-morning -- the famous Piazza San Marco by 80 centimetres.
Workers set up elevated walkways as sirens and loudspeaker announcements reinforced the alert. Under a new system, warnings and updates were also being sent out by text message.
The tidal centre predicted earlier that floodwater would fall back to normal levels by 7:00 pm (1800 GMT), but said another surge was expected in the small hours of Tuesday.
The situation was complicated by a national transport strike affecting the city's "vaporetto" water bus service.
Experts said the surge in the sea level was caused by a combination of persistently high southerly winds and heavy rain and snowfall in northern Italy over the past few days.
Venice was flooded 50 times between 1993 and 2002, with the worst incident on November 4, 1966, when the city was submerged by 1.94 metres of water amid catastrophic flooding throughout Italy.
More recently, in February 1986, levels reached 1.58 metres above normal. The last time the waters passed 1.60 metres was in 1979 when they reached 1.66 metres.
The city has for years been wrestling with the problems posed by the threat of rising sea levels. In March, local authorities confirmed they were looking at a scheme to raise the city's buildings to meet the problem.
Under Operation "Rialto", local officials and engineers were looking at using piston-supported-poles placed at the bottom of each structure to lift buildings by up to to a metre.
They calculated it would take around a month per building if each structure was raised by eight centimetres (3.14 inches) a day.
In April 2007, the United Nations cultural organisation UNESCO warned that Venice was one of its designated World Heritage sites that was threatened by climate change.