A riot broke out in Cardiff on Monday night at the scene of an earlier vehicle crash.
Videos shared on social media showed a large crowd of people gathered around a fire on a road in Ely, while riot police faced the crowd in an attempt to control a “large scale disorder”.
Objects were reportedly thrown at police, and the windscreen of at least one service vehicle was smashed.
At least six police vans were called to the scene, while officials urged people to avoid the area. A police helicopter was also dispatched.
People were gathering items of rubbish and furniture, including chairs and sofas, to add to a fire in the middle of the road, Wales Online reported.
They were also pushing breeze blocks off garden walls and carrying them into the road, according to the website.
Fireworks were reportedly set off, while police with dogs attempted to move the crowd back.
A serious road crash was reported on Snowden Road shortly after 6pm, police said.
Unverified posts on social media later speculated that the collision had been caused by a police chase.
Police urged people “not to speculate” online, and said the crash had already happened before officers arrived.
In an statement on Twitter, South Wales Police Cardiff said: “Police are continuing to monitor and respond to disorder in Ely. A number of vehicles have been set alight. Arrests are being made. A large police presence remains in the area.”
Earlier, the force said there were “a large number of officers working to manage the collision”, but also to “de-escalate ongoing disorder at the scene”.
“We urge anyone involved to leave the scene immediately and ask local residents to stay away while the matter is brought to a safe conclusion,” police said.
“Emergency services remain at the scene. It is important that people avoid the area so we can effectively deal with this incident.
“Please avoid speculation – we will bring you the latest details as soon as we can - all of our updates must be factual.”
The rioters continued to throw missiles and set cars alight into the early hours on Tuesday.
One resident of Highmead Road, who did not want to be named, said: “Enough is enough now. This has gone beyond.
“When people are making fun of what's happening on social media it's crossed a line.
“This is our neighbourhood and those doing this are just kids. It needs to stop.”