A footpath row between two mothers sparked the new outbreak of sectarian violence which erupted in flashpoint North Belfast, police said.
Officers moved in to break up a confrontation after a Catholic mother on her way to collect her daughter from Holy Cross Primary School was challenged by a Protestant woman.
It was then that trouble broke out, flaring into the worst street disorder in Belfast for several months.
By the time it ended early today, 14 police officers and several civilians were injured. At the height of the disturbances there were up to 500 rioters on both sides, but just three arrests made.
Paramilitaries using mobile phones were accused of orchestrating the trouble and at least one senior member of the republican movement was heavily involved in attacks on troops.
Several cars, one belonging to the police were destroyed.
Nearly 140 petrol and acid bombs, as well as bricks, bottles and fireworks, were thrown.
Seven people were hit by plastic bullets fired by police, and four Catholic men needed hospital treatment after being wounded by shotgun pellets.
The school at the centre of the bitter row was closed today as politicians and churchmen on both sides called for calm.
Extra police and troops have been moved into the district, but there are fears that this latest trouble could escalate and even spread to other parts of north Belfast where Protestant and Catholic live just yards apart in some areas.
Today streets near the school were covered in rubble, inches deep in parts, and burned out vehicles.
Protestant residents who protested at Catholic parents from neighbouring Catholic Ardoyne bringing children to school through their area suspended their action late last year when a series of measures was agreed to try to keep the lid on the trouble.
But it was the confrontation between two mothers yesterday afternoon which triggered the trouble, according to Assistant Chief Constable for Belfast Alan McQuillan.
At one stage some of his officers had to draw their weapons to hold back Protestants trying to break their way in the school grounds.
He said today: "Police had to intervene. They attempted to make an arrest. At that point a person (a Protestant) was rescued by a crowd and within a very short time of time we had crowds from both sides out on the streets."
Mr McQuillan added: "The trouble start spontaneously, but once you scratch the surface the paramilitaries are never far away."
Staff at Holy Cross will meet later today, but it is not yet known if the children will return to class tomorrow.
The school is in the middle of the Protestant Glenbryn district.
Closing it down is not an option, according to Father Aidan Troy, chairman of the board of governors.
He said: "That is not the sort of message we want to send out.
"Everyone of goodwill wants to keep the school open and move the situation forward, but the tensions here today are worse than ever.
"We had hoped this was all over, but it looks as if everything is lost."
Meanwhile there were reports of loyalists attacking cars at the Catholic Lady of Mercy Secondary School in the predominantly Protestant Ballysillam area of north Belfast.
Police officers were at the scene, which is around half a mile from Holy Cross School.Reuse content