The First Minister of Wales, Mark Drakeford, says "unacceptable" disturbances in Swansea on Thursday night will not be tolerated.
Several cars were set on fire and pushed down a steep hill in the Mayhill district of Swansea. Footage of the events popped up on Instagram and Snapchat.
When police intervened, they were pelted with missiles by a crowd of thugs and were forced to retreat.
A local newspaper showed images of two cars on fire in the middle of the street as a crowd gathers and cheers.
It was estimated that 200 people became involved in the riot, which reportedly began after youths gathered at a vigil for a young man who died earlier this week.
Ethan Powell, 19, a keen football fan, collapsed after watching Swansea City’s play-off match with Barnsley on television.
The Chief Constable of South Wales Police, Jeremy Vaughan, said he was both “saddened and furious” by the trouble.
South Wales Police issued a statement at 10.45 p.m. on Thursday, 20 May, which said: “A number of our officers are at the scene of large-scale disorder in the Mayhill area of Swansea. Residents are urged to stay indoors while the matter is brought to a safe conclusion”.
The incident is not believed to have been politically motivated, and the rioters have been described on social media as “yobs.”
Some residents of Mayhill are furious at the police for failing to protect them.
Adam Romain told the BBC he feared the "mob" would enter his home and attack him, his girlfriend and their two small children after he confronted them and tried to stop them setting fire to his car.
Mr Romain said: “Bricks were starting to be lobbed at me and my house...my children were in the house, my girlfriend was in the back screaming, scared for their lives. I was standing at the front, hoping, praying, that they wouldn't come inside the house”.
Nobody was injured or killed in the disturbances but South Wales Police have vowed to catch those responsible.