The mountain road has been closed as police urge people to leave the scene
Five people have been arrested following an “illegal gathering” of about 200 people.
South Wales Police said officers remained at Rhigos Mountain in Cynon valley as it urged people to leave area.
The force has put a dispersal order in place giving officers powers to move people on.
Rhigos Mountain pass in Rhondda Cynon Taf has been closed in both directions, traffic analysts Inrix confirmed.
“For public safety reasons, please do not attend on foot or in vehicles,” said a police statement.
“There are currently road closures in place.”
