Police officers and fire-fighters came under attack from a group of up to 50 youths last night after apparently being lured into a nationalist estate in the Co Antrim town of Ballymena.
Several cars were set alight and stones were thrown at the emergency services during the disturbances in Dunclug Park, which local SDLP councillor Declan O'Loan said were orchestrated.
Calm eventually returned to the area at around 3am after several hours of rioting.
The PSNI said no officers were injured and no arrests were made.
Mr O'Loan said the trouble was linked to annual celebrations by the Ancient Order of Hibernians.
Meanwhile, police are investigating a motive for a petrol bomb attack on a post office depot in Derry last night.
Two postal vans were damaged when up to four devices were thrown over the wall of the depot on Little James Street.