The network of 78 bright yellow barriers that guard the entrance to the delicate Venetian lagoon started to lift from the sea bed more than three hours before the high tide was scheduled to peak.

The tide, driven by strong winds and heavy rains, was expected to touch 130 cm (4.27 ft), well below the devastating the 187 cm tide that battered Venice last November but enough to leave low-lying areas deep under water.

Officials will be hoping the controversial, multi-billion-euro flood defence system, known as Mose, will mitigate the pending storm.

Designed in 1984, Mose was due to come into service in 2011, but the project was plagued by the sort of problems that have come to characterise many major Italian construction programmes -- corruption, cost overruns and prolonged delays.

It was finally tested in July and engineers deemed it was ready to use in bad weather.

Venice’s floods, “acqua alta” (high water) in Italian, are caused by a combination of factors exacerbated by climate change - from rising sea levels and unusually high tides to land subsidence that has caused the ground level of the city to sink.

Once operational, the Mose system is designed to protect Venice from tides of up to 3 metres, well beyond current records, but some experts worry it will be overwhelmed by the sort of rising seas that recent climate-change models have predicted.