Danish police tear-gassed and arrested on Monday more than 150 demonstrators who had set alight barricades outside a giant Copenhagen squat, police said.
Demonstrators threw petrol bombs at police who tried to move in and put out the fires, who responded by launching tear gas.
Police with dogs then entered the Christiania squat, detaining "between 150 and 200" people, police spokesman Henrik Suhr told AFP.
"We entered into Christiania to pursue individuals who had built the barricades, set alight the fires in the streets and threw fire bombs at our police officers before taking refuge in Christiania," he explained.
A large number of Danish and foreign climate activists participated Monday in a party in Copenhagen's "free city" of Christiania, a refuge for hippies and artists since the 1970s.
A witness interviewed on TV2 News said police had blocked all the exits from Christiania and then fired tear gas and raided the tent where the party was taking place.
Police earlier Monday made 17 arrests at a rally attended by more than 1,000 climate activists demanding the opening of borders to climate refugees.