Three people were arrested when a New Year's Eve rave party at an industrial estate in Bristol turned to violence.
The event, promoted on the social media site Facebook, was being held at South Liberty Lane.
Police said at its peak, more than 1,000 illegal ravers attended, breaking into commercial premises, occupying buildings, setting fires and throwing bottles at officers.
The arrests were made for public order offences and damage.
A spokesman for Avon and Somerset Police said officers were working under "sometimes exceptionally violent and difficult circumstances to bring the situation under control".
Police broke up the party at about 1100 GMT on Saturday.