"It started out as a peaceful demonstration but then there was more and more violence and the riots against the police started," Munch said.
The Danish Ritzau news agency reported a police spokesman as saying that the police had "never arrested so many people in a single incident before".
Police estimated the number of demonstrators as between 1,000 and 2,000, while organisers said there were as many as 4,000 people.
The authorities fired tear gas at the demonstrators, while protesters hurled smoke bombs and tried to break through police barriers and climb over police cars.
No injuries were reported, according to the police, and demonstrators failed to occupy the unused waterworks owned by the city of Copenhagen.
In March, the forced eviction of squatters running the Ungdomshuset centre, a haven for the city's youth and its underground culture since 1982, sparked several nights of violent protests in the capital.