VENICE, Italy — Exceptionally high tidal waters rolled relentlessly through Venice again on Friday, forcing the closure of St. Mark’s Square to the public and flooding most of the lagoon city’s already devastated center before easing.

Forecasters warned that the danger for more wind-propelled high tides remained through the weekend.

The Italian government issued an international appeal for donations to help repair damage to the centuries-old city’s rich cultural heritage after Tuesday’s floods, which were the worst in decades.

People can donate 2 euros ($2.20) by sending a text message to a special number Culture Minister Dario Franceschini said.

“All the world loves this splendid city, let them show it now,’’ he said in a statement.

A senior port authority official wrote to major cruise ship companies to for donations.

Massive cruise liners disgorge thousands of day-trippers into Venice on a near-daily basis, boosting its economy but also risking accidents with smaller vessels.

Late Tuesday, Venice water levels reached 1.87 meters (6 feet, 1 inch) above sea level, the highest flooding since 1966.

On Friday, ten minutes before noon, the tide peaked at 1.54 meters (5 feet) above sea level. Six hours later, it had receded to some 60 centimeters (two feet).

Built on a series of tiny islets amid a system of canals, Venice is particularly vulnerable to a combination of rising sea levels due to climate change coupled with the city’s well-documented sinking into the mud. The sea level in Venice is 10 centimeters (4 inches) higher than it was 50 years ago, according to the city’s tide office.

More than 50 churches have reported damage from the tides, Minister Franceschini said as he inspected the city. Carabinieri officers from the corps’ world-renowned and highly-trained squad of art experts were being deployed to map damage to art treasures, a job that is expected to take some time.

“While the water is still there, it’s difficult to know what the [full] damage is,” Franceschini said.

The minister called on lawmakers of all political stripes to quickly approve extending tax breaks for those who donate to help restore state monuments and artworks and also for those who contribute for Venice’s damaged churches.

“There are so many churches which have suffered damage and were invaded by water,’’ Franceschini. Likely the most heavily damaged was St. Mark’s Basilica, since it is in one of the lowest points of the city.

At the government’s request, the Italian Space Agency was gathering radar data from satellites to detect any signs that Venice bell towers may have shifted or that their foundations might have weakened after being buffeted countless times over the centuries by fast-rising waters.

On Thursday, the government declared a state of emergency, approving 20 million euros ($22.1 million) to help Venice repair the most urgent damage.

Venice Mayor Luigi Brugnaro has estimated damage at hundreds of millions of euros and blamed climate change for the city’s plight.

He also called for the speedy completion of the city’s long-delayed Moses flood defense project. Moses consists of a series of moveable barriers in the lagoon that can be raised when high winds and high tides combine to threaten to send “acqua alta,’’ as the uniquely Venetian phenomenon is known, rushing across the city.

Completion of the multibillion-euro project, under construction since 2003, has been delayed by corruption scandals, cost overruns and opposition from environmentalists who were worried about its effects on Venice’s delicate lagoon ecosystem.

Opposition politicians in the Veneto Region, which has Venice as its capital, noted wryly that the local center-right majority had just voted against an amendment to fund efforts aimed at dealing with climate change when the regional assembly hall was flooded Tuesday night, forcing politicians to flee.

While tourists sloshed earlier in the week in St. Mark’s Square or strolled across it on strategically placed raised walkways to witness the water rushing into ancient St. Mark’s Basilica, on Friday, the mayor said he asked police to block off the square, which covered in water up to adults’ knees.

University students in Venice rushed to libraries and other institutions filled with books and manuscripts to help shift the material to higher stories. Improvising, at least one volunteer used a hair dryer to dry a valued volume, page by page.

The Italian Society of Authors and Editors, which said Venice’s book stores and libraries were “gravely damaged” by the high water, launched a fundraising campaign. Pitching for donations from Italy and abroad, the group said it was important to “take the side of those who every day are on the front lines for the defense of Italian culture.”

It said one Venice bookstore, poignantly named “Acqua Alta” (High Water), had been completely submerged by the rushing water.

Venice’s La Fenice opera theater was left unusable by the flooding. Milan’s opera theater, La Scala, said it would mount a special ballet on Nov. 29 to raise funds for La Fenice.

Giada Zampano and Frances D’Emilio contributed from Rome.