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.

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 two euros (2.20 U.S. dollars) by sending a text message to a special number, Culture Minister Dario Franceschini said. 

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.

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.

Likely the most heavily damaged was St. Mark's Basilica, since it is in one of the lowest points of the city. 

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

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 November 29 to raise funds for La Fenice.