By Christy Cooney & Jared Evitts & Tomos Morgan
BBC News
Two teenage boys died in a crash before a riot broke out in Cardiff which left several police officers injured.
Cars were set alight and fireworks thrown at police as 100-150 people gathered at the scene in Ely on Monday.
Police dismissed social media rumours that they were involved in the crash, saying officers arrived at the scene afterwards.
The link between the crash and the disorder was unclear, South Wales’ police and crime commissioner said.
“It would appear that there were rumours, and those rumours became rife, of a police chase – which wasn’t the case,” Alun Michael said.
“And I think it illustrates the speed with which rumours can run around with the activity that goes on on social media nowadays – and that events can get out of hand.”
Mr Michaels said up to 12 officers were injured in the disorder, which started on Snowden Road.
The force said its thoughts were with the families of the two boys who had died as well as those affected by the subsequent disorder.
A number of people have been arrested and “more will follow”, a police spokesperson said.
“Our focus now is to fully investigate the circumstances of the collision and the appalling scenes that followed”.
Mr Michael told BBC Radio 4’s Today that the crash in which the two teenagers died was “being investigated in its own right”, but that it appears to have sparked the disorder.
He said that the connection between the two events was “far from clear”.
“So obviously there’s going to be investigations going on this morning to try and establish what happened”, Mr Michael said.
Police said that, shortly after 18:00 BST, officers responded to a report of a “serious road traffic collision” on Snowden Road.
The force said the crash “had already occurred when officers arrived”.
Two police cars were damaged in the disorder, with pictures showing one with its windscreen broken and its wing mirrors hanging off.
A member of the public was also attacked because some of those gathered thought they were an undercover police officer, according to one of the senior officers at the scene.
At least two parked cars were set alight, one of them after being tipped onto its roof.
Snowden Road was closed between Wilson Road and Jackson Road with drivers asked to avoid the area.
John Urquhart, who lives in Ely, witnessed the incident escalate from the start of the evening.
He said the vast majority of people were in the street because they “wanted to know what would happen next”, and added that there was “a very small number of people actually doing any sort of violence.”
Mr Urquhart said he was very “counter-violence” and offered first aid to people during the evening.
In a tweet at 01:10 BST, police said they were “continuing to monitor and respond” to the situation and that a “large police presence remains in the area”.
As the disorder continued into the early hours of the morning, those gathered moved down nearby Highmead Road as police attempted to disperse them.
Police, including officers on horseback, were seen outside Ely police station amid suggestions that it could be targeted.
The National Police Air Service also said it had assisted with the incident.
On Tuesday morning, paving stones and pipes could be seen strewn across the street.
Other parked cars had had windows smashed, while a child’s car seat lay in ruins on the road.
‘Crossed a line’
Jane Palmer said she and her family watched from a window as people outside set fire to her car.
“I’m disabled so now I’m trapped without my car,” she said.
“Why are they doing this? It’s just silly now.”
Another resident, who did not want to be named, said those behind the violence were “kids”, and that it had “crossed a line” and “needs to stop”.
In an earlier post, police urged “anyone involved [in the disorder] to leave the scene immediately” and asked local residents to “stay away while the matter is brought to a safe conclusion”.
“We need to ensure that this evening’s collision is effectively investigated,” they said.
They also asked local residents to remain indoors.
Cardiff Bus said earlier that a service it runs through the area had been re-routed and would remain so for the rest of the evening.