Fifteen people have been arrested after a police station in Norfolk came under siege in the early hours from a crowd of 100 people hurling bottles.
About 100 people hurled beer and wine bottles at the building
The attack in Great Yarmouth happened after police arrested three people in a van carrying sound equipment.
Police said 200 officers from across the region then broke up an "unlicensed music event" at a warehouse on Harfrey industrial estate just before midday.
Forty-four cars were seized at the event, a police spokesman said.
The attack on the police station was declared a major incident by Norfolk Police and Ch Supt Bob Scully said: "We acted swiftly to control the situation and restore order.
"What occurred was entirely unacceptable and inexcusable.
"This was large scale anti-social behaviour and officers dealing with the incident were put at serious risk.
"It is behaviour that won't be tolerated."
Two police vehicles were damaged and officers narrowly avoid serious injuries, police said.
More than 100 officers from Norfolk, Suffolk, Essex and Cambridgeshire police forces took part in the operation, which finally ended at 1030BST.
People have been warned to stay away from the Harfrey industrial estate, which is being treated as a crime scene.