Police were still trying to break up an illegal rave in Yate, near Bristol, more than 14 hours after being called to the site.
Avon and Somerset Police were informed of the event at a warehouse in Millbrook Road around 10.30pm on Saturday.
Officers arrived within 12 minutes of the call and found several hundred people and a number of vehicles. A dispersal notice was issued requiring them to leave.
Units from the dedicated team dealing with unlicensed music events were deployed and roads were closed, but large numbers continued to arrive on foot.
“A number of the people being prevented from entering the premises became hostile towards the police. Items, including lit spray cans and bottles, were thrown at police, some of whom were injured but remained on duty,” the force said.
“A secure cordon was put in place by 4am, but it is estimated that approximately 500-700 people were on site. While a number of people have left, it is believed a significant number remain within the premises.”
Western Power attended and cut electricity to the building but an alternative source was found by the rave organisers.
Police asked for help from neighbouring forces to try to close down the event, and two people have so far been arrested.
Chief Inspector Mark Runacres said: “This has been an incredible challenging operation with a large number of people in a confined space and several officers being assaulted.
“We are working with neighbouring forces and the ambulance service to look to bring this event to a close in a controlled way that does not jeopardise the safety of people in the area.
“We’re sorry for the disruption caused by the selfish actions of the organisers of this event and those attending. This unlicensed event was organised in secret, despite people being fully aware of the ongoing risk to public health due to Covid-19.
“Their actions were wholly irresponsible and I am sure will disgust the overwhelming majority of people who are making huge sacrifices to limit the spread of the virus.
“Our investigations team will be involved in reviewing officers’ body-worn footage and other inquiries as we seek to take appropriate action against those responsible.
“We’d ask anyone with evidence and information that can help, to call 101 and quote log number 1369 of October 31.”
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