Twenty-two police officers have been injured and their vehicles damaged during clashes at an illegal street party in south-west London.
Two officers and two partygoers were taken to hospital following the “unlicensed music event” near Angell Town in Brixton on Wednesday night.
Police were called after complaints from residents about noise and violence. Four people were arrested.
Home Secretary Priti Patel described the scenes as “utterly vile”.
A dispersal order had been put in place earlier in the day and police officers tried to encourage the crowd to leave.
The event continued so more officers attended and the group became hostile, the Met Police said.
Footage on social media showed a number of police vehicles being smashed and officers being chased.
Another video also appears to show two men being attacked with a knife.
London Ambulance Service said two partygoers were taken to hospital in police vehicles, with one needing treatment at a major trauma unit.
Four people were arrested for assault and public order offences. They remain in custody.
Cdr Colin Wingrove said: “These gatherings are unlawful, as well as posing a risk to public health and against coronavirus restrictions.
“The violence shown towards officers is totally unacceptable and we will not tolerate it in any form.”
Police later implemented a Section 60 order, which gives increased stop and search powers.
One witness said people from outside the area had come to Angell Town and caused problems.
Michael, a local bus driver who did not want to give a his surname, said it was “very upsetting” the violence had happened in his area.
“The whole thing should have been shut down earlier,” he said.
He blamed people from other areas who “come down to tarnish the works and efforts that have been put into the area by the estate management”.
Ken Marsh, chairman of the Metropolitan Police Federation, said nearly 30 of his colleagues were “walking wounded”.
“No-one expects this level of violence and hostility to just erupt at the speed it does towards police. It’s horrendous,” he said.
He also raised concerns about large gatherings when lockdown is eased and pubs reopen on 4 July, saying “ultimately it always seems to fall on the police’s shoulders to deal with everything”.
“There is no place in society for disorder and wanting to cause violence and pain and grief towards public and police alike,” Mr Marsh said.
Ms Patel tweeted: “Just last weekend, the whole country came together to praise our heroic police officers for putting their own lives on the line to keep us safe.
“I’ll be picking up with the Met Commissioner immediately.”
The Mayor of London Sadiq Khan said: “Violence against the police will not be tolerated.
“Large gatherings during Covid-19 are deeply irresponsible and risk others’ lives.”
Mr Khan said he was in touch with police about the incident.