Eighteen police officers and a number of marchers and their supporters have been injured during trouble at an Orange Order parade in north Belfast.
Water cannon were deployed by police during clashes
Stones were thrown at marchers by nationalists on the return leg of the Tour of the North parade as they passed a flashpoint area at Ardoyne.
Six petrol bombs were thrown as police used water cannon to regain order.
PSNI District Commander, Chief Supt Mike Little, said his officers had come under "sustained attack".
Trouble flared at about 2100 BST as three lodges, followed by supporters, went past Ardoyne shops where nationalists had gathered to protest against the march.
Marchers had been separated from the protesters by a corridor of about 60 Land Rovers and police in riot gear, but were still pelted with missiles, including bottles, bricks and golf balls.
There were further clashes between police and protesters and the water cannon were deployed. Six petrol bombs were then thrown.
Stones were thrown at police and marchers
Chief Supt Little described the trouble as "extremely disappointing" and said officers would be investigating a breach of the Parades Commission ruling by the protesters.
"We will be examining CCTV footage from the scene and will work to bring all those found breaking the law to justice," he said.
The march was the first to be affected by an extension of the law governing the behaviour of parade supporters.
It gave police wider powers to control the movement and behaviour of parade followers at flashpoint areas.
The Tour of the North is among the first of a series of parades by Protestant Orangemen which culminates in the biggest demonstrations on 12 July.
A ruling by the Parades Commission had restricted nationalist protesters to the footpath outside the Ardoyne shops and loyalists supporters also face restrictions, following conflict at a parade last July.