Police used tear gas on Monday in clashes with rock-throwing rebels protesting the demolition of a decrepit building in Copenhagen's hippie enclave.
At least 16 people were arrested, police said, while one police officer and one protester were injured.
The protesters set fire to a barricade on the main road outside the Christiania district of the Danish capital, sending thick, black smoke into the sky. Helmeted riot officers fired tear gas at masked youths hurling bottles and cobblestones.
The clashes erupted two months after angry youths went on a rampage in downtown Copenhagen to protest the eviction of a squatter from a youth center in another part of the city. Hundreds were arrested and some 25 people injured.
Police spokesman Flemming Steen Munch said youth activists who took part in those riots also joined Monday's clashes in Christiania, which started after workers started tearing down a condemned building.
The wooden structure, known as Cigarkassen - or the cigar box - had been used by homeless people after being damaged by a fire in 2002.
Residents of Christiania, who have been protesting the government's plans to end the small district's alternative society, had called for peaceful protests against the demolition.
But the situation spun out of control when black-clad youths built a large barricade and set fire to it to keep police from entering the area.
One demonstrator was injured in a scuffle with baton-wielding police officers after he punched an officer's helmet. The protester was handcuffed and taken away by ambulance, bleeding from his forehead.
Munch said the man had a cut to his eyebrow, but the injury was not serious and that the man would be charged with assaulting a police officer after being treated.
Christiania was founded in the 1970s when hippies proclaimed their freewheeling society on state-controlled land behind Copenhagen's old ramparts. They painted the buildings in psychedelic colors and advocated free marijuana, nudity and anarchy with no cars and no police.
Parliament recognized Christiania as a "social experiment" in 1987, and four years later gave the residents the right to use the land.
However, lawmakers three years ago adopted the center-right government's plan to end the social experiment. The government wants to create a housing agency to assume ownership of Christiania's buildings, impose rents and allow outsiders to move in.