Violence erupted in the western port city of Patra in the early hours of Thursday as self-styled anarchists clashed with supporters of the neofascist Golden Dawn party, reports said.
One restaurant and four cars were damaged during the clashes. There was no report of injuries.
Two police cars arrived at the scene, but police did not intervene, according to witnesses.
The clashes came a day after allegations that supporters of Golden Dawn have routinely taken part in the police's Xenios Zeus sweep operations across the city.