Police in Northern Ireland say 26 officers and two members of the public have been injured during what they describe as significant public disorder in Belfast city centre.
Five of the 26 officers were taken to hospital.
The disorder first flared in the Royal Avenue area, a usually busy shopping district close to City Hall, as hundreds of loyalist demonstrators gathered to protest at the rally to mark the introduction of internment in Northern Ireland during the Troubles.
The organisers of the Anti-Internment League parade had been given permission for the event from the Parades Commission adjudication body.
As loyalists attempted to block the route, riot police were attacked with a sustained barrage of bricks, bottles, fireworks, metal guttering ripped from shop fronts and pint glasses apparently raided from a nearby bar.
Unrest soon spread as the parade approached from north Belfast. There were reports of clashes involving loyalists and republicans close to a junction leading to the unionist Shankill Road, while a number of parked vehicles were set on fire in the nearby North Street area.
Police deployed water canon and fired more than 20 plastic baton rounds in a bid to quell the disorder.
The parade was unable to pass down Royal Avenue as intended. After a significant delay, it did finally proceed along the outskirts of the city centre and onward to west Belfast.
However, trouble continued in its wake.
A republican parade finally reached its destination following hours of disturbances in Belfast.
Police Service of Northern Ireland Assistant Chief Constable George Hamilton condemned those responsible for the violence.
"Whilst facilitating the Parades Commission determination for tonight's parade and associated protests, police have come under heavy and sustained attack by crowds intent on creating disorder," he said.
"As Northern Ireland moves ahead, the effect of tonight's violence has the potential to damage the local economy and the reputation of Belfast as a tourist destination.
"As disturbances are continuing, I would call upon people of influence in communities and those in political leadership to do all possible to reduce tension."
The trouble in Belfast has broken out at an unfortunate time for tourist chiefs and civic leaders as the city is currently hosting thousands of international visitors attending the World Police and Fire Games.
Less than a month ago, parts of Belfast were consumed by rioting, predominantly loyalist, triggered when Orangemen were prevented from parading past the nationalist Ardoyne area in the north of the city.
The latest disorder comes after eight officers were injured when trouble flared at a republican anti-internment bonfire near the city centre last night.
Eight people were arrested and at one point, as violence spread to north Belfast, officers were attacked by a man wielding a sword.
There is also controversy surrounding a planned commemoration event in Castlederg, Co Tyrone this Sunday for local IRA members killed during the Troubles.