A number of police and a unionist MP have been injured as loyalists clashed with officers amid serious outbreaks of violence across Belfast.
At least four police officers were injured after sectarian tension spilled over into violence. DUP MP Nigel Dodds was also taken to hospital after being hit on the head by a missile.
Four were taken to hospital for treatment - three of which were knocked out while another suffered head and leg injuries.
In north Belfast, violence broke out between police and loyalists in the Woodvale area close to Ardoyne following the return leg of an Orange Order parade. Bricks and bottles were thrown as officers attempted to hold back crowds of protesters. Officers were pelted with bits of masonry, bottles and other missiles during clashes with loyalists.
Water cannon was deployed amid heavy rioting which broke out close to the north Belfast flashpoint. There were also reports of several plastic bullets being fired as well as men wielding swords attacking officers.
The Police Federation has said officers "continue to be attacked by rioters in several parts of Belfast. A number of officers (all PSNI) injured."
Meanwhile water cannon has been used in an attempt to quell violence which has broken out in the Lower Newtownards Road area of east Belfast.
Missiles have been thrown at police during ongoing trouble.
Tonight, Sinn Fein's Martin McGuinness laid the blame at the door of the Orange Order.
The deputy First Minister Martin McGuinness tweeted: "Responsibility for tonight's violent attacks on Police & the community rests with the Leadership of the Orange Order, they are a disgrace."
The Orange Order called for calm on the streets.
On Twitter a spokesman said: "The Parades Commission must go but violence is not the way to achieve it. All protests must be peaceful."
The trouble in north Belfast began after bands passed by St Patrick's Catholic church on their return leg.
Although there was no initial violence, tensions soon led to scuffles with police close to York Street.
It's understood a number of nationalists had spotted a crowd of bandsmen
A group ran towards the area before throwing police cones.
Police then mobilised and formed a barrier between the groups.
Sinn Fein MLA Gerry Kelly blamed the violence in the Woodvale area on the Orange Order and unionist politicians.
"Speech after speech at the various (Orange) demonstrations were clearly designed to stir up sectarian tension and have alongside the Orange Order's failure to abide by Parades Commission determinations led directly to the violence in Belfast tonight.
"No amount of hand wringing or denial in the coming days from the Orange Order and unionist politicians can alter that reality.
"People had a right to expect better, instead what we got was a very deliberate strategy with the inevitable results being seen on the streets this evening."
DUP MLA Nigel Dodds was also struck on the head by a missile and taken to hospital for treatment.
Speaking earlier this evening the North Belfast representative said: "This sort of situation here creating a bottleneck at this junction, the Parades Commission decision to block it here, this is the inevitable outcome.
"The police were well aware that was the danger the Parades Commission had put them in. I would appeal for everybody to stay calm, not to get involved in violence. The Grand Lodge have made it clear they do not want violence and the people who want to engage in violence should desist immediately."
Loyalist bandsmen - many highly intoxicated - played sectarian songs at police lines while bricks and bottles were thrown.
At one point a rioter broke down a section of wall and threw it at police shields.
Others used sticks and pieces of drainpipe to batter police vehicles while some danced on top of the force's Land Rovers and tried to rip off protective plating.
Justice Minister David Ford has condemned those involved in attacking police officers.
"The international image of Northern Ireland post G8 has been seriously damaged by the scenes of rioting in the Woodvale area this evening," he said.
"I have spoken to the Chief Constable throughout today and I would like to thank the PSNI and their mutual aid colleagues for the great job they are doing in protecting lives and trying to maintain order. I would also like to express my sympathy to the PSNI officers injured in tonight's violence."