ROME — The mayor of Venice, who said that the city “was on its knees,” has called for a state of emergency and the closing of all schools after the Italian city was submerged under “acqua alta,” an exceptionally high tide — the highest in 50 years.

Outdoor restaurant tables and chairs could be seen bobbing in the waters, and tourists were forced to clamber through the windows of high-end hotels as the water rose to about six feet before 11 p.m. on Tuesday.

As dawn broke on Wednesday, the authorities began to survey the damage.

“I’ve seen things in San Marco I thought I’d never see,” Mayor Luigi Brugnaro of Venice told the Italian station Radio24. “It is a very difficult situation,” he added.

In a post on Twitter, the mayor blamed climate change for the city’s troubles and called for the rapid completion of a long-delayed barrier system.