Hundreds of people who ignored Covid rules to attend an illegal rave in a city centre have been condemned as "selfish and dangerous".
People were seen singing and dancing along to a DJ set at the Castlefield Bowl outdoor arena in Manchester on Wednesday evening.
Greater Manchester Police (GMP) said officers were trying to find out who organised the gathering.
Councillor Pat Karney said the people were "letting Manchester down".
"If you play live music at any of these gatherings your equipment will be seized," said the Labour councillor, who is an associate member of the Manchester City Council executive.
Castlefield Bowl is used for outdoor concerts or gatherings such as a live screenings of football matches.
On Tuesday, Heath Secretary Matt Hancock tweeted to say "don't blow it" as thousands gathered to enjoy the weather in outdoor spaces, prompting social distancing concerns.
GMP said officers spent all of Wednesday patrolling the Castlefield Bowl area and "were continually monitoring and engaging with groups of individuals to engage, explain and encourage compliance with the Covid rules and regulations".
The force said music equipment was set up as numbers increased in the evening.
"As officers attempted to engage with a group at the scene they were met with hostility causing them to withdraw," a spokesman said.
GMP said the gathering was "swiftly dispersed" when reinforcements arrived.
No fixed penalty notices were issued "but inquiries are ongoing to locate the organiser", the force added.
Assistant Chief Constable Chris Sykes condemned the "disgusting and appalling" behaviour.
"I accept it has been hard but rules are rules," he said.
Insp Jonathan Shilvock said the gathering was a "clear breach" of coronavirus rules and regulations.
"We appreciate that people will want to socialise due to the warm weather and the recent relaxation of the rules, but I want to remind people that this pandemic is not over and we all share a collective responsibility in complying with the rules and keeping infection rates down," he said.
Councillor Rabnawaz Akbar, executive member for neighbourhoods, said the easing of lockdown restrictions did not allow for public spaces to be left in "disgraceful state" by "selfishness pure and simple".
By Thursday morning, volunteers and council contractors had removed 58 bags of waste.
Mr Akbar urged people to "be considerate and to either put rubbish in the bin, or take it home with you".
"It was encouraging to see so many people come out to help clear up, it is frustrating they had to do this in the first place," he said.
Gary Rumens, from Castlefield Litter Pickers which helped with the clean up, said residents were "disappointed and angry".
"We're got a tight-knit community and to see such an open space like this being used like this is upsetting," he said.
Lynne Cade, who lives nearby on a boat, said she was "extremely tired" and "very tearful" after the illegal rave and was planning to move out of the area.
"My boat is my home and my sanctuary and I'm extremely anxious now," the university lecturer said.