Venice was under water on Tuesday as heavy rain and strong winds pushed into the lagoon city, catching the authorities off guard before they could activate the huge flood barriers that were rolled out just two months ago.

A flooded St. Mark's Square in Venice, Italy on Tuesday Photo: VCG

The system of 78 flood gates, known as Mose, guard the entrance to the Venetian lagoon and are designed to protect the city from tides of up to three meters. However, they require 48-hour notice in order to be activated.

Weather bulletins in past days had forecast rainfall pushing sea levels up to 120 centimeters, below the 130-centimeter threshold at which the flood barriers are operated.

Luigi Brugnaro, the city's mayor, said on Twitter that the weather had suddenly worsened and water had reached a 145-centimeter peak as strong sirocco winds blew in from Croatia and two rivers flooded near the sea around Venice.

He called for more rapid and reactive protocols in the operation of Mose in order to face sudden weather changes.

"The situation is terrible, we are under water," said Carlo Alberto Tesserin, responsible for managing Saint Mark's Basilica, adding that if the water rose further all the internal chapels would be flooded.

The center for tidal forecasts in the Venice area said the water would recede to 120 centimeters on Wednesday and be back up to 135 centimeters on Thursday.

High tides, or acqua alta in Italian, have been regular occurrences in Venice over the years, caused by a combination of factors exacerbated by climate change.