At least 60 people were injured and 130 arrested during extremist rallies in the German city of Hamburg over the weekend, police said on Sunday.
Hundreds of rioters took to the streets on Saturday night after an alternative Left-wing street festival, attacking passers-by and smashing cars and shop windows.
The previous night, 12 policemen and several protesters were injured as right-wing National Democratic Party (NPD) followers threw stones, bottles and lit fires in protest ahead of the Left-wing event.
Hamburg Senator Christoph Ahlhaus spoke of an "enormous potential for violence", and said the police had responded decidedly to criminal offences.
One police officer fired a warning shot as around 30 people armed with iron bars and wooden beams had descended on the police.
"Thankfully, it was just a warning shot," said Duty Officer Peter Born, adding that the consequences for the city would have been unthinkable had the situation escalated further.
Similar events occurred in other German cities at the weekend.
In Hannover, around 3,000 people took to the streets on Saturday in protest at a 270-strong NPD rally.
In the former East German state of Thuringia, 550 people protested against a right-wing music festival which had drawn around 370 NPD followers to the town of Poessneck.
Senior politicians have called for the NPD to be banned, after an attempt to do so in 2003 failed when it was revealed that large numbers of the party's inner circle were actually undercover government agents or informants.