Groups of up to 30 youths are causing havoc on a busy street by climbing onto roofs and free-running in what police described as "an accident waiting to happen".
Police have ramped up patrols along Holton Road in Barry to stop the youngsters, some of whom are as young as 12, from causing any more trouble.
In one incident, four youths, aged between 12 and 14, were stopped by police after kicking in a window near a 30-40ft drop while others were spotted doing back flips on roofs.
Officers from South Wales Police have said the consistent anti-social behaviour is "an accident waiting to happen" and is alarming those living and working in the area.
One business owner, who did not want to be named, said the problem had been going on for as long as he could remember.
The man, who said he had lived in Barry all his life, owns one of the businesses on Holton Road and said he constantly sees "lots of drugs, violence and fighting" and it was getting worse.
"I've seen them setting fire to cardboard boxes outside the shop," he said.
"It's got a lot worse recently and they are hanging around in bigger groups."
Officers have warned the youths, who are mostly teenagers, that their risky behaviour is "endangering themselves whilst causing anti-social behaviour as well as breaking coronavirus rules".
PC Helen Kihlberg said: "A group of youths have persistently been committing anti-social behaviour on Holton Road in Barry by climbing business roof tops and free-running, which is not only breaking coronavirus rules at present but is also putting their safety at risk.
"It is an accident waiting to happen, which would mean emergency services are stretched even further, at a critical time within the pandemic.
"There have been up to 25-30 youths at one point and their general activity has the potential to cause criminal damage to the structure of the properties and is causing members of the public to be alarmed and concerned about their safety as some youths were doing back flips off the roof."
The police force said some individuals had already been identified and anti-social behaviour referrals had been submitted to the Vale of Glamorgan Community Safety Partnership who have carried out Anti-Social Behaviour stage warnings.
PC Kihlberg added: "We are also stepping up our police patrols in the area to take further action if required and we are therefore reminding these youths to refrain from this activity and to follow the Welsh Government coronavirus rules."
Anyone with information is asked to call police on 101.
