Rostock police used tear gas and water cannon to combat masked protesters who pelted them with Molotov cocktails, rocks, bottles and sticks. Sky News reported 25 officers suffered serious injuries and 17 demonstrators were arrested. CNN pegged the number arrested at 50.

The violence erupted when about 500 demonstrators descended on police after a series of largely peaceful marches involving tens of thousands of people throughout the city.

"The police were attacked massively from the violent protesters," police spokesman Frank Scheulen said.

Police estimated the size of the overall protest at 25,000, but organizers said it was 80,000.

"There were thousands of people and most were absolutely peaceful," one witness, Lexi Barnett, told The Sunday Herald. "It was only when we got to the end of the rally we realized a lot of the more radical, extreme protesters were involved ... and a lot of people had to move out of that area quickly."

The protest was organized by several dozen groups under the motto "another world is possible," Fox News reported.