Tourists in Venice were barred from an inundated St Mark's Square on Monday, as fierce winds and rains lashing much of the country drenched the floating city.
Venice city officials say 70 percent of the lagoon city has been flooded by waters rising 149-centimetres above sea level.
The "acqua alta" (high water) peaked at 156-centimetres by early afternoon, the elevated wooden platforms usually placed on main passageways in the city were not enough to ensure safe passage in the low-lying square.
The current level is the highest reached since November 2012, according to Venice statistics.
The last time levels topped 160 centimetres was in December 1979.
The Venice Marathon on Sunday saw several inches of water at certain points of the course in the race.
Much of Italy is under alert for flooding from heavy rains, a problem exacerbated by a lack of maintenance on river beds.
Veneto regional governor Luca Zaia says flooding could reach the levels of the 1966 flood that inundated both Venice and Florence.