Large numbers of young people have gathered in a seaside town, leading to outbreaks of disorder and antisocial behaviour, police say.
South Wales Police said it had authorised a "section 35 dispersal order" for Barry Island on Wednesday, and had confiscated alcohol.
The order gives officers the power to exclude people from an area for 48 hours to prevent crime.
People intent on causing trouble should "stay away", police said.
"Our officers have been called to a number of disturbances in the Barry Island area this evening. It is a place enjoyed by people of all ages, at all times of the day, and such behaviour won't be tolerated," said Ch Insp Michelle Conquer.
"Officers will be maintaining a visible presence in the area and our officers will proactively deal with any issues that arise.
"Our message to anybody intent on going to Barry Island to cause trouble or behave in a way that law abiding people will find offensive, is to stay away."
What is a dispersal order?
- It can be used for a maximum of 48 hours to prevent crime or disorder or to stop people being harassed, alarmed or distressed
- It must have regards for normal rights of freedom of expression and freedom of assembly.
- People can be asked to leave a locality or specific part within it and not to return for the period of the order
- There are various restrictions around access to homes and places of work, which are set out under section 35 of the Antisocial Crime and Policing Act 2014