There was a heavy police presence in Pontypridd on Friday after large groups of youths gathered in the town centre.
People reported seeing large groups of young people in the town centre on Friday night and some were seen travelling there by train from other parts of Rhondda Cynon Taf.
South Wales Police said they knew about a planned "large gathering of young people" in Ynysangharad Park but said the public should not be concerned and that no offences have taken place.
They said they were contacted by concerned residents and that large groups of youths have now been dispersed.
A spokesman said: "Some youths from all over the Rhondda valley decided to meet up in Pontypridd. We had been warned in advance of it happening.
"We were made aware of a planned large gathering of young people in Ynysangharad Park.
"We would like to thank the people who called us with their concerns.
"Thanks to this information we were able to prepare for this gathering and this resulted in a large groups of youths being dispersed peacefully.
"We understand it can seem intimidating but no offences have been committed."
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Rachel Locke said: "I drove through a gang of hundreds of kids about 6.30pm running out of Ponty park across the main road, and a load heading towards the train station."
One person posted in Trallwn and Coedpenmaen Community Page: "I just walked home through town. It's surreal. I've never seen so many teenagers in one place."
One woman said: "I have just been down to the town centre. There were different groups of 20 and 30 young people. There is also a heavy police presence."
