Police say they did not have the manpower to stop an illegal rave near Bath which attracted more than 3,000 partygoers through the night.
The event, at the former RAF Charmy Down airfield about three miles from the city, began late on Saturday.
People living as far away as Bristol complained they had been kept awake.
Avon and Somerset Police said despite officers arriving at the scene within minutes of being alerted there were already "many people at the site".
Ch Supt Ian Wylie said the force was aware a major gathering was likely this weekend, but it was unable to pinpoint where it might take place.
Once officers were called to the former RAF station, he said, it was too late.
'No standing army'
"We got the call just after 23:00 (BST) and we were there within 10 minutes but all the stages were set up and all the music was already going with many, many people at the site," he said.
"It became impossible for us to do anything... because of the safety of those partygoers, many of whom were drunk, many of whom were on drugs, and the safety of the officers attending."
He said it was not possible to gather enough officers to disperse such a large number of people at that time of night.
"We don't have a standing army waiting to deal with these issues," he added.
In an earlier statement, Avon and Somerset Police said despite closing off approach routes, officers were still turning vehicles away on Sunday morning.
Ch Supt Wylie said the music was stopped just after 13:00 on Sunday and the site was eventually cleared three hours later.
Local resident Dulcie Walpole said as well as the noise issue, the arrival of huge numbers of cars had also caused disruption.
"We had appointments to go to this morning and we couldn't actually get out of the lane, there were cars parked all the way down and it's all blocked off," she said.
"All of our neighbours have called the police and complained and it doesn't seem to have done anything."
Given up trying to sleep - illegal rave that @ASPolice seem powerless to stop has kept much of Bath awake most of the night. I would advise sending them packing soon - there are a lot of angry, sleep deprived locals.— Adam Joinson (@joinson) July 19, 2020
Tanya Rich, who lives in Weston in Bath, said the music from the rave, held close to the A46, woke her up at 05:00.
"I heard this thumping sound. I thought someone had their car stereo on loud and it would stop, but it kept going," she said.
"I went on my local Facebook group and everyone was talking about it and complaining.
"People have been saying they can hear it as far away as Longwell Green, even Kingswood.
"It's so loud. You couldn't have a window open."
Ch Supt Wylie said an investigation would take place into how the rave was organised.
"This is just, frankly, selfish actions of individuals who seemed determined to ignore the Covid-19 legislation, and all of the health advice that has been widely publicised," he said.
"They have caused significant disruption to the people of Bath and the local area."