Two police dogs were also injured during the altercation after the “Wild n Out” music show at Ealing Town Hall was shut down after 11pm due to overcrowding.
According to one organiser, 2,000 people had turned up to the 600-capacity venue.
Rioting is thought to have broken out soon after in nearby Longfield Avenue with officers making several arrests as they fought to bring the mob under control with support from the Met’s Territorial Support Group.
Roads were closed off and buses diverted while officers attempted to control the violence.
Police surrounding the McDonald’s in Ealing after violence broke out.
The Somali Wild n Out was lit. It was fun, it was great energy and good vibes. Just a few idiots that caused the show to be locked off
One Twitter user, Holly wrote: “There’s armoured police outside McDonald’s in Ealing Broadway it’s all kicking off.”
Another added: “There was an event tonight, then it got locked off and like 1,500 roadmans flooded Ealing. So it kicked off I guess.”
One of the event’s promoters posted his thoughts after the night descended into chaos.
“This event was my dream, it was going so well, never did I expect almost 2,000 people to attend a venue that holds 600… I did my best,” he said.
Music fans on social media have since praised the event and condemned the violence which followed.
“The Somali Wild n Out was lit. It was fun, it was great energy and good vibes. Just a few idiots that caused the show to be locked off,” said Jay.
Another user said: “The Somali Wild n Out actually looked lit from the snaps, it’s sad how Somalis have to spoil it for themselves.”
Police are yet to release details of the arrests but the injured officers did not require hospital treatment and the dogs were seen by a vet.
A Met Police spokesman said: “A number of youths had tried to attend an event being held at the town hall but could not gain entry because the event was full.
“Officers from Ealing borough attended. The decision was taken to shut the event down and disperse the crowds.
“The groups then descended on nearby Longfield Avenue where disorder broke out.”
He added: “A number of people have been arrested for public order offences.”