Riots flared again last night between rival nationalist and loyalist crowds after earlier confrontation outside Holy Cross School as pupils were returning home.
Plastic bullets were fired by police and two people were reported injured.
Shortly before 9 p.m. rioters from both sides of the sectarian divide began attacking the police and army with fireworks and other missiles. The number of police officers injured rose to 14.
Despite a heavy police and security force presence in the area in an attempt to keep apart rival factions, people from both communities showed little sign of wanting to disperse.
Both the First and Deputy First Ministers, Mr David Trimble and Mr Mark Durkan, condemned the disturbances saying the violence would solve nothing. In a joint statement they said they were "deeply disturbed to see the renewed scenes of violence in north Belfast after the progress which has been made in recent weeks".
Northern Secretary Dr John Reid described yesterday's events as a "tragedy".
"It would be a tragedy if the progress made last year was squandered and it would be a tragedy if the children and the decent people of north Belfast were to have their reputation betrayed by people acting like thugs. The people of Northern Ireland deserve better."
Local political and community leaders in Ardoyne will be working today to prevent a repetition of the violence which erupted in north Belfast yesterday. Holy Cross School will remain closed for the day because the board of governors believes it is not safe for the children to attend classes.
The trouble began when nationalists and loyalists threw stones, bottles and fireworks at each other and at police. A police car was destroyed by a loyalist petrol bomb.
Sinn Féin MLA for North Belfast, Mr Gerry Kelly, claimed the trouble re-started when two people were struck by police Land Rovers. He blamed loyalists for the violence and said unionist politicians must "get it under control".
Four civilians were treated in hospital after earlier incidents - three of whom are understood to be nationalists who sustained pellet wounds. Although there are reports of earlier tensions, the situation deteriorated when Catholic parents were jostled and spat upon as they walked up Ardoyne Road to collect their children yesterday afternoon. Loyalist protesters gathered outside the gates and pupils were prevented from leaving.
They were bused home after police arrived. Loyalists held a 12-week protest outside the school last year. It was called off in December after an initiative from Mr Trimble and Mr Durkan. Local community and political representatives agreed a series of housing, traffic, educational and financial measures to calm tensions but loyalists last night predicted the protest could resume.
Father Aidan Troy, chairman of Holy Cross Board of Governors, said everything should be done to avoid this and stressed the seriousness of the situation. "We are not back to square one, it is worse than that. It will be very, very hard to come back from this but we will have to try."
Father Troy will be meeting Holy Cross teachers today to discuss the school's next move. The North's Education Minister, Mr Martin McGuinness, expressed "deep concern" for the pupils and said local political and community leaders must engage in "honest dialogue" to prevent escalation.
The North's Security Minister, Ms Jane Kennedy, condemned the actions of "mindless thugs" and said children should never "have to pay the price of the failure of adults to live together".
Local DUP councillor, Mr Nelson McCausland, claimed nationalists had started the trouble by attacking a Protestant school bus. "The violence emanated from the republicans. They are engineering it for political and propaganda purposes. We must not allow this to happen. I appeal to everyone to remain calm and vigilant."
Progressive Unionist Party Assembly member, Mr Billy Hutchinson, also blamed nationalists. "Apparently a young guy bumped into a Holy Cross parent as she was coming down the road. She took exception to this and called on a group of men to intervene. They wrecked five cars and then tried to wreck houses."
Protestant community worker, Mr Mark Coulter, claimed the trouble started when Catholics pulled a wreath from a lamp-post which commemorated a Protestant killed by republicans.
Mr Trimble and Mr Durkan called on "everyone in the area to step back and to consider the impact further violence would have on their communities".