EXTRA Garda patrols will be placed at Portmarnock beach over the weekend after a riot involving up to 40 youths fighting and firing bottles broke out.
It's understood the incident escalated after two gangs clashed at around 4.30pm yesterday.
"It all started with one group of lads slagging off another group of lads," one eyewitness told the Herald.
"There was a fight between two of them and then all the lads rowed in. Beer bottles were being thrown and there were up to 40 of them there.
"Units of the gardai took a significant quantity of alcohol off underage drinkers."
One youth was restrained and three arrested last night.
A shop owner put the number of revellers at more than 1,000.