Riots in parts of Belfast were on a scale not seen in Northern Ireland in recent years, a police chief has said.
PSNI Assistant Chief Constable Jonathan Roberts said police are investigating whether there was any paramilitary involvement, given the level of pre-planning and orchestration.
Police came under sustained attack after more than 600 people gathered at an interface between loyalist and republican areas.
Petrol bombs, bottles, masonry and fireworks were thrown during the scenes of violent disorder in west Belfast.
Police fired six plastic bullets – known as attenuating energy projectiles or AEPs – on Wednesday night.
Eight officers were injured and two men aged 28 and 18 were arrested on suspicion of riotous behaviour.
Mr Roberts said the scenes of riotous behaviour in Northern Ireland were “disgraceful”.
He also said that children as young as 13 and 14 were involved, who were being encouraged and supported by adults who stood by and clapped.
Speaking at PSNI headquarters in Belfast, Mr Roberts said: “The scale of the disorder last night was at a scale that we have not seen in recent years in Belfast or further afield.
“The fact that it was sectarian violence and large groups on both sides is not something we have seen in recent years. We believe there was a level of pre-planning.
“The crowds grew in numbers and attacked each other with multiple petrol bombs and multiple missiles, including masonry and fireworks, and attacked police.
“The scenes we saw were disgraceful in terms of the seriousness of criminal acts that were being carried out and the violent disorder.
“We also saw a bus being hijacked, it was an extremely distressing incident for the bus driver and the people on the bus at the time.
“We had two other vehicles set on fire and pushed against the gates.
“It is very lucky that no-one was seriously injured given the large volume of petrol bombs that were thrown. Anyone who participates in such behaviour can expect to be arrested and remanded into custody and placed in front of the courts.
“I can’t confirm the involvement of paramilitaries but the orchestration of last night’s disorder and the previous nights is the subject of investigation.”
Mr Roberts also said the use of AEPs is not a tactic police want to use.
He added, however, that given the “potential for imminent loss of life”, it was a tactic that was deployed on Wednesday night.
Police said they are also aware of other events and protests that are planned in the coming days.