At least four blast bombs have been thrown at police in east Belfast, it has been confirmed.
Several petrol bombs were also hurled after disturbances broke out in the Lower Newtownards Road area on Monday.
The Police Service of Northern Ireland (PSNI) said there were no reports of any injuries. At least one plastic bullet was fired and water cannons have been deployed to quell the disorder.
A PSNI spokeswoman said: "Police are currently dealing with public disorder in the Lower Newtownards Road area of east Belfast this evening.
"At least four blast bombs and several petrol bombs have been thrown at police. There are no reports of any injuries at this stage. Water cannon has been deployed and one AEP (attenuated energy projectile) round has been fired by police.
"Police would appeal for calm in the area and would call on those with influence to do what they can to help restore calm."
Earlier, a pipe bomb packed with nails was thrown towards police lines in north Belfast.
The device was hurled from the nationalist Brompton Park area of Ardoyne and exploded after striking an armoured police vehicle just after 5pm. There were no reports of any injuries.
Witness Sam Coulter, who was yards from the explosion at a loyalist protest, said it was fortunate no one was hurt.
He said: "We were standing having a peaceful protest when all of a sudden there was a bang and the next thing we heard the 'tinkle, tinkle, tinkle' of nails dropping on the ground.
"I think it was directed at the protest - police were at the other side of the road behind a Land Rover. Luckily nobody was hurt - just a bit of a bang to the ears.
"The place is in lockdown now with police doing sweeps of the area to gather evidence.
"This won't put us off our protest - we are still here."
Sinn Fein MLA for North Belfast Gerry Kelly claimed a seven-year-old child was on the street when the bomb was thrown.
"The first thing to say is that this attack is completely unacceptable and is not supported by the vast majority of the community in Ardoyne and I condemn it. It is wrong and it should never have been carried out. It was a cynical attempt to try and attack the police and raise tensions in the nationalist community in this area which has up to now been calm," he said.
PSNI Superintendent Emma Bond said: "We consider ourselves extremely fortunate that we are not dealing with a much more serious incident and that all of the officers were able to walk away from that situation unharmed. We have appealed for calm in the area and I continue to do so. I would appeal to anyone with influence in the community to exert it to ensure that the next few days pass off without incident.
"An investigation is now under way into tonight's events and I would appeal to anyone who has information to contact us."
The Crumlin Road has been closed between Tennent Street and Twaddell Avenue and diversions have been put in place.
Terry Spence, chairman of the Police Federation, which represents rank and file officers in Northern Ireland, said police were in a difficult position.
"We have been here so many times before where the police are the meat in the sandwich. Quite clearly this demonstrates how police officers have to be alert and very cautious looking over their shoulder while carrying out public order duties. They can come under gun or bomb attack at any stage. It is a worrying development but sadly it is not new," he said.
SDLP MLA for North Belfast Alban Maginness also condemned the attack.
He said: "After three nights of violence in north Belfast the PSNI have now been subjected to a pipe bomb attack in Brompton Park in Ardoyne. This is completely unacceptable and I am very glad to hear that no one was injured in this needless and cowardly attack.
"This is a time now for cool heads and I would urge restraint on the community lest the violence that we have witnessed over the past few nights spread and grow."
There has been a large police presence in north Belfast since violence erupted on Friday after Orangemen were prevented from marching on a contested stretch of road past the nationalist Ardoyne area.
Last year a republican gunman opened fire on police in the same area during rioting which broke out after the annual Orange Order parade was permitted to go ahead.
An additional 1,000 police officers have been drafted in from forces across the UK to help keep peace on the streets of Belfast, and PSNI Assistant Chief Constable Will Kerr said hundreds more would be brought in over the coming days if parade-related violence continued.
DUP MLA for North Belfast William Humphrey described the pipe bomb attack as an attempt to kill.
"'This nail bomb was not only a deliberate attempt to further inflame tensions in this area but was an attempt to cause death or serious injury. Fortunately despite this indiscriminate weapon exploding, no injuries were sustained.
"Local people have already suffered enough as a result of the trouble within the area. There is absolutely no justification for violence from any quarter, and I would hope that this incident will be treated with the utmost seriousness."
Theresa Villiers, Secretary of State for Northern Ireland, added condemnation.
"This was a deplorable attack on police officers which I totally condemn," said Ms Villiers.
"This highlights once again the dangers faced by PSNI and the courage they show in protecting the whole community. They should have the full support of everyone in Northern Ireland."