Belgrade: Vast blocks of ice, moving freely on the Danube after a sudden weekend thaw, crushed and sank dozens of boats, pontoons and floating restaurants in Belgrade yesterday, and many others — lodged in ice — were carried downstream.

Temperatures in Serbia rose from minus 20 degrees Celsius (minus 4 degrees Fahrenheit) last week to 10°C on Sunday, melting packed ice more than 30cm thick, after weeks of freezing weather that has affected most of Europe.

Boat owners at the Kapetanija marina in Belgrade's picturesque Zemun neighbourhood tried to winch boats and pontoons from river, boat owner Mihailo Svilaric told Reuters.

"We are trying to salvage whatever we can, only a handful of boats remained intact from about a hundred we had in the marina," Svilaric said. Debris was scattered among the breaking ice for more than a kilometre along the river and several floating restaurants, barges and boats were torn from their moorings and beached on riverbank as fast-moving ice snapped anchor lines.

"The ice was so fast that we could do nothing to prevent this," said boat owner Dragan Jovanovic. "The damage will be hundreds of thousands of euros for sure."

Serbian authorities had used icebreakers on the Danube, Sava and Tisa rivers, but the ice built up too quickly and port authorities halted traffic on all waterways on February 8.

At least 20 people have died from cold in Serbia in the last few weeks. Economists say damage from the cold snap may cost Serbia, already suffering the effects of the Eurozone debt crisis.