Nine police officers have been injured during public disorder at a flashpoint in North Belfast.
Nationalist youths rioted for hours after a loyalist march on a contentious stretch of road.
The teenagers went from hurling missiles to ramming police lines with vehicles they had stolen.
Officers deployed water canon and later fired plastic bullets in an attempt to restore calm.
Nigel Dodds, the Democratic Unionist MP, witnessed the unrest in his constituency.
“There comes a point where everybody has to stand up against people who only are interested in violence,” he said.
The Orange Order had been told it must complete its annual parade earlier than usual.
Loyalists were outraged when the Parades Commission then permitted a nationalist protest march on the road.
Tension reached breaking point when rival factions came face to face, exchanged chants and threw bottles at each other.
Not for the first time, police were caught in the middle.
Gerry Kelly, a Sinn Fein member the Stormont Assembly, said: “Let’s sit down, talk this out and come to some sort of accommodation. We have had worse problems to solve.”
North Belfast witnesses similar disturbances every July but they are now being fuelled by a power struggle.
Sinn Fein had called for calm but dissident Republicans made no such appeals.
Assistant chief constable Will Kerr, the officer in charge of policing parades in Northern Ireland, encouraged “individuals and communities” affected by trouble to respond in a “calm and responsible manner.”
With the Orange Order demanding its right to walk traditional routes and Catholic residents objecting, the marching season often provides the backdrop for a period of tension on the streets.
Loyalists march to mark the victory of King William of Orange over the Catholic King James in 1690.
To some, it is tradition; to others, triumphalism and they rarely compromise.