Police say they are continuing to deal with an illegal rave at a warehouse near Bristol.
Officers who were called to Yate at around 22:30 GMT on Saturday said up to 700 people were in attendance.
Some of the crowd began acting violently towards officers as they were told to leave, Avon and Somerset Police said.
The crowd was ordered to disperse and police said two people were in custody.
A force spokesman said when officers arrived they “found a number of vehicles and several hundred people” at the site.
“Roads approaching the area were closed to prevent more people reaching the site by car but large numbers of people continued to arrive on foot from several different directions,” he said.
The spokesman added 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,” he said.
“A secure cordon was put in place by 4am, but it is estimated that approximately 500 to 700 people were on site
Power was cut to the building but an alternative source was being used, the spokesman said.
“Additional resources have been sought this morning from neighbouring forces to support our response as we seek to bring the event to a close as soon as possible and safely disperse those remaining on site.”