Armed riot police moved in tonight to remove nationalist protesters staging a sit-down demonstration ahead of an Orange Order march.
The major security operation at the Ardoyne shops interface in north Belfast saw officers in body armour try to clear the Crumlin Road of more than 100 people who had been there from mid-afternoon.
Their initial attempts were resisted but the efforts were ongoing.
The protest at the notorious flashpoint was organised to prevent Orangemen marching along the road on their way back from the annual Protestant Twelfth of July commemorations.
Meanwhile, bomb disposal experts are examining a hijacked bus that was left outside Woodburn police station.
Two masked men reportedly got on the vehicle in the Glencolin Walk area around 4pm, told the driver a device had been left on the top deck and ordered him to drive to the station.
A car was later hijacked in the Oldpark Road area and found abandoned on Alliance Avenue where officers were examining it.
Tonight's marches follow overnight rioting in north Belfast in which 27 officers were wounded.
One policeman remained in hospital today after he and two colleagues were hit with pellets from a shotgun fired by a masked man who emerged from a crowd of nationalists who attacked the police.
Another 24 officers sustained injuries in two separate flashpoints in north and south-west Belfast.
Police said water cannon and baton rounds had to be used after the trouble began at about 11.45pm.
Police said none of the injuries were life-threatening. The policeman who remained in hospital was being treated for shotgun pellet wounds to his arms and upper torso.
Police presence is high at potential interface areas today amid fears of further disturbances. About 100 nationalists have staged a sit-down protest in the road at the Ardoyne shops interface in north Belfast where an Orange parade was due to pass this evening.
The thoroughfare has been the scene of violent clashes on the Twelfth over recent years and the police presence was again high amid fears of a repeat this year.
Northern Ireland?s Justice Minister David Ford condemned the rioters. ?News of what happened last night, with the police coming under gun and petrol bomb attack, will anger people across Northern Ireland,? he said.
?Those responsible for last night?s trouble are to be condemned and it is clear that there is a small minority of people who want to create havoc and do whatever they can to raise tensions and heighten fears within the community.
?I would urge those who have influence to show leadership and do whatever they can to bring calm to the streets.?
Chief Superintendent Mark Hamilton also criticised those responsible for the disorder and attacks on his officers. ?These officers were doing their jobs, were policing their local community and have been attacked whilst doing so,? he said. ?This is utterly wrong and I condemn it in the strongest possible terms.
?We responded to this disorder immediately and officers put themselves in danger in order to restore normal and calm to the area for the residents who live there. No one wants a return to this type of behaviour.
The annual Twelfth of July marches commemorate Prince William of Orange's victory over Catholic King James II at the Battle of the Boyne in 1690.
PA