Police found a crowd of around 100 children - some as young as 12 - drinking at an illegal outdoor party in south Belfast.
The children were drinking in Lagan Meadows in a secluded area of woodland near the river, the PSNI said.
Alcohol - including bottles of vodka, beer and cider - littered the woodland, where residents say music was heard playing late into the night.
The PSNI said officers found around 100 children aged between 12 and 16 drinking area.
But a spokesman added that the trouble was not limited to under-age drinking.
He said: "Sadly, the Fire Service also had to be tasked to put out some gorse fires. The area is very dark, has barbed wire fences, and is beside a river. Listen, I don't want to be a killjoy, but equally, I don't fancy pulling someone out of the river and I am sure you agree the fire service has more important calls to attend."
A message posted online by PSNI South Belfast asked parents: "Do you know where your children are tonight?"
Residents near the area said the trouble appeared to start at around 9pm and finished close to midnight, when police arrived on the scene.
They said the parkland has recently become a hotspot for drug dealers and over the last year has become a regular spot for parties.
One man told the Belfast Telegraph how the trouble had caused concern to a mother with two teenagers living nearby.
He said: "She worries about it because of her boys - they thought they were buying into a safe, trouble-free neighbourhood and now they've got to worry about their sons and make sure they are not getting involved in this.
"I told police yesterday that my neighbours were concerned.
"Several of the emails I got from them while I was on holiday were about this trouble here and what is going on; it's just casual comments, but it has been going on for a while.
"There are noisy weekends. There are parties there and there is a lot of drink taken up to them."
He added he had seen police car chases and car searches in the area as police tried to tackle the issues.
Another man who lives in the area criticised the way police were dealing with the under-age drinking issue.
He said: "Obviously police are coming so often because residents are complaining, but they will never get anyone unless they go up there in plain clothes."
He added that he had seen suspicious activity in the area which he believed was linked to drug dealing.
No arrests were made following Saturday night's incidents.