At least 15 people have been injured in running battles between youths and police in the northern German city of Hamburg, officials say.
The clashes lasted for several hours, Hamburg police say
The clashes began when a large group of suspected left-wing radicals set fire to rubbish bins after an annual street festival on Saturday night.
The police said water cannon and batons had been used to disperse the rioters. Thirty-eight people were detained.
The Shanzenviertel festival attracts thousands of people every year.
The clashes lasted for several hours, after the rioters erected street barricades and set ablaze rubbish bins.
At one point a four-metre-high (13-ft) fire was burning in the city, police spokeswoman Karina Sadowsky was quoted as saying by the AFP news agency.
"It is all over now," she said, adding that eight of the injured were police officers.
Officials said at least 5,000 people attended this year's festival.