A car smoulders during clashes between police and nationalist youths in the Ardoyne area of north Belfast July 12, 2011. Twenty-two police were injured when Irish nationalists rioted in Northern Ireland overnight, burning cars and firing petrol bombs to protest annual marches by pro-British Protestant groups. [Photo/Agencies]

BELFAST - Police fired plastic bullets and water cannon at Catholic youths in Northern Ireland's provincial capital Belfast on Tuesday after rioting erupted when a Protestant parade passed their estate.

Sporadic violence erupted across the British-ruled province on the culmination of a season of parades by pro-British Protestants to mark a 17th-century military victory, a tradition many Catholics say is provocative.

Around 200 people threw bottles, slates and petrol bombs in the mainly Catholic Ardoyne area of Belfast after police moved in to prevent them confronting the passing Orange Order parade.

Two cars were set on fire and dozens of rounds of plastic bullets were fired. Police said a number of officers were injured.

Most of the 500 or so parades across the province passed peacefully, but police reported rioting in Londonderry, Newry and Armagh as well as the Markets area in central Belfast.

Three decades of fighting between mostly Protestant loyalists who want Northern Ireland to remain part of the United Kingdom and Irish nationalists, mainly Catholics, who want it to be part of a united Ireland tore the province apart during a three-decade period known as the "Troubles."  

A 1998 peace agreement paved the way for a power-sharing government of loyalists and nationalists. Violence has subsided, but police say the threat from dissident groups opposed to the peace deal is higher than it has ever been since it was signed.

A small Orange Order parade passed the Ardoyne estate in near silence with one drummer keeping time after a government commission ordered marchers not to play their traditional drums or flutes.  

A few dozen residents held a silent protest as they passed, while a small group of women sang the Irish national anthem.

But hundreds of others were pinned by police vans and officers in riot gear into an estate a hundred metres (yards) from the marchers, a move residents said was heavy-handed.

"It's the same thing every year. It's aggravation," said Jim, a 47-year old health worker watching the parade. "We're surrounded up here. It's no wonder the kids have so much hatred."

Marchers were marking King William of Orange's victory over the Roman Catholic King James at the Battle of the Boyne in 1690, which helped to secure Protestant supremacy in Ireland.

Pipe bands and drummers from Scotland joined local groups decked in orange banners and British flags for hundreds of marches across the province.

"It's a celebration, we don't want any trouble," said Eddie Whyte, 42, as he marched past Belfast City Hall on Tuesday morning. "If they are offended by the British flag, maybe they shouldn't be living in this country."  

Two dozen police officers were injured in nationalist rioting on Monday night as Protestant youths lit hundreds of bonfires, many draped in Irish flags, to mark the July 12 holiday.  

Catholic and Protestant politicians have called for calm in recent days and urged people not to go into the streets to protest against the parades.  

"We must not allow the progress that has been made to be thwarted by those who want to drag us back to the past," Northern Ireland's First Minister Peter Robinson said.

Police said they had also come under attack on Tuesday evening in the mainly Catholic Markets area of Belfast, with rioters throwing bricks and fireworks and setting a car on fire. A car was hijacked and set alight in Armagh.