At least 47 police officers have been injured after being attacked by Republicans and Loyalists during a Nationalist parade in north Belfast.
Bricks and stones were thrown at police lines in the Carlisle Circus and Clifton Street area as they separated the two sides late last night.
Police briefly used a water cannon to quell the disturbance.
Four of the officers were taken to hospital, but three had been released by the morning.
A spokeswoman for the Police Service of Northern Ireland said: "Police are urging all individuals and communities affected to take a step back. Violence has serious and unwanted consequences for us all."
Officers said disorder was significant but localised.
Sinn Fein MLA Fra McCann said a house in West Belfast was petrol bombed at around 5.30pm yesterday in a sectarian attack.
"There are five children who live in this house and this can only be described as attempted murder by those responsible," he said.
"There are fears that this is an escalation to the repeated attacks on these homes given the use of petrol bombs and the ongoing situation in north Belfast."
North Belfast was the scene of serious rioting on July 12 when Republicans attacked police following a Nationalist parade through the Ardoyne flashpoint.
The summer marching season has polarised communities in north Belfast for many years, but despite this most loyal order parades across Northern Ireland pass peacefully.
Unionists are bitterly opposed to the Parades Commission, which rules on where controversial marches can go and places conditions on them.
Northern Ireland First Minister Peter Robinson has said he is considering reopening efforts to deal with parading after a recent bid for a new deal collapsed following discussion with the Orange Order.