About 200 people gathering for an illegal rave in woodland overnight were dispersed by police.
The party at Eston, on Teesside, was broken up at about midnight.
Cleveland Police described the rave as “unacceptable” and warned such events pose “potential safety concerns”.
It came as people across England had their first night out in three months after coronavirus restrictions were eased.
Sgt Paul Higgins said people had been arriving in taxis ahead of the rave.
“It’s the first night of the pubs opening so we weren’t expecting to get an illegal music party.
“We found a number of people here. There hadn’t been anything set up yet with any music or equipment but they’ve been dispersed.”
Police had earlier issued a warning on social media urging people not to attend the event.
In UK law, an illegal rave is when 20 or more people are “gathering on land in the open air” with music “that includes sounds wholly or predominantly characterised by the emission of a succession of repetitive beats” – at a level where it is loud enough to cause “serious distress to the inhabitants of the locality”.