Loyalists blocked roads across Belfast as part of a mass protest over flags.
The pickets caused disruption for rush-hour traffic. Bus operator Translink suspended most of its Metro services into and out of the city centre.
Social media websites listed up to 60 protests across Northern Ireland to start from 6pm on Friday. A PSNI spokeswoman reported at least 10 roadblocks.
She said: A number of roads have been closed due to ongoing protests. These currently are Templemore Avenue; Albertbridge Road; Upper Malone Road at the Dub Lane; Crumlin Road at Cambrai Street and Hesketh Park; Limestone Road at North Queen Street and the Boyne Bridge off Sandy Row."
The PSNI later confirmed all routes across Belfast were reopened after the protests. There were no reports of any disorder.
It is the 19th day that loyalists have taken to the streets to show their opposition to restrictions on flying the Union flag over Belfast City Hall. Most have been peaceful but sporadic violence has marred some of the demonstrations.
Meanwhile, two people were arrested after reports of disorder in east Belfast during the early hours of Friday morning.
Police said a group of about 15 men attacked houses in the Lower Newtownards Road area. A family left their home because of the attack.
A 27-year-old man was arrested for possession of an offensive weapon and is due in court in January. A 20-year-old man was arrested for riot.
Superintendent John McCaughan, of the PSNI, said: "Tensions are heightened; however, we would ask that people take a step back and consider the wider implications of engaging in any criminal behaviour."