At least two RUC officers were injured when serious loyalist rioting broke out in north Belfast tonight.
Police fired plastic bullets at rioters after blast bombs, petrol bombs and fireworks were hurled at them on the Crumlin Road.
The RUC said at least 300 people were involved in the trouble which they described as "serious disorder".
Two officers were taken to hospital for treatment and the extent of their injuries was not immediately known, said an RUC spokeswoman.
Trouble started after loyalists blocked the Crumlin Road near the Ardoyne shops to stage a protest.
Earlier loyalist protesters threw fireworks at the parents of the Holy Cross schoolchildren in north Belfast.
Parents from the Catholic Ardoyne area were on their way through the neighbouring Protestant Glenbryn district to collect pupils when the fireworks were thrown, police said.
Nobody was hurt in the incident.
Sinn Fein claimed loyalist paramilitaries had threatened to shoot the parents. The firework attack had caused widespread panic and distress and was part of a campaign to drive nationalists out of the area, they added.
Sinn Fein councillor Ms Margaret McClenaghan said: "Those who carried out this attack can only be described as sick."
The trouble broke out when crowds taking part in what had been a peaceful protest on the Crumlin Road tried to force their way up the road to Brookfield Mill where Catholic workers had a narrow escape earlier in the day when an explosive device was thrown into the yard where they were standing.
RUC Assistant Chief Constable Alan McQuillan said: "Once again we have seen disgraceful scenes of disorder in north Belfast."
He said many RUC officers had to be deployed and had to fire plastic bullets because of the nature and scale of the violence.
Mr McQuillan appealed to public representatives to do all in their power to "return some sort of sanity to this situation".
PA