A man has died of a suspected drug overdose and three others were stabbed as thousands attended two illegal raves in Manchester on Saturday night.
The 20-year-old man had been at a large gathering of about 4,000 people in Droylsden, according to Greater Manchester Police.
There were reports of three separate stabbings at another rave in nearby Carrington involving about 2,000 people, police said.
An 18-year-old man suffered life-threatening injuries – and two other men, aged 25 and 26, were also injured.
A 25-year-old man was arrested on suspicion of possession of an offensive weapon, police said.
Officers said they are also investigating the rape of an 18-year-old woman who attended the Carrington event.
Police were met with violence from participants at the party, with items thrown and a police car vandalised.
On Sunday, Assistant Chief Constable Chris Sykes said: “We are aware of two large raves that took place in Carrington and Droylsden last night.
“These raves were illegal and I condemn them taking place – they were clearly a breach of coronavirus legislation and guidelines, and have had tragic consequences.”
He said the emergency services experienced a “surge in emergency calls”, with more than a 60% increase in demand via 999 calls from 5pm on Saturday night to 4am this morning.
Mr Sykes added that violence towards police at the Carrington rave was “absolutely not acceptable and will not be tolerated”.
“Our officers are working incredibly hard to keep people safe and should never be met with inexcusable violence whilst carrying out their duties,” he said.
Deputy Labour Leader and MP for Ashton-under-Lyne Angela Rayner tweeted: “Those who attended put themselves and their loved ones at risk. (Completely) irresponsible.
“A lot of effort went into online events this weekend across (Greater Manchester). Those who attended should be ashamed of themselves. My local area now has to deal with the aftermath.”