BELFAST- Violence flared for a second night around traditional Orange Day parades in Northern Ireland, with police coming under attack from petrol bombs, fireworks, stones and bottles and responding with water cannon.

Loyalists throw bottles at police in the Woodvale Road area of North Belfast, on the second night of violence after an Orange Parade was blocked from marching past the Nationalist Ardoyne area in Belfast, July 13, 2013.[Photo/Agencies]

One police officer was engulfed in flames when struck by a petrol bomb, but it was quickly extinguished by colleagues. The officer remained on duty after being examined by medical personnel, a spokesman said.

Thousands of pro-British Protestants march every summer in the British province, a regular flashpoint for sectarian violence as Catholics, many of whom favour unification with Ireland, see the parades as a provocation.    

Violence between the two religious groups still sometimes flares since a peace deal was signed in 1998, which largely ended three decades of strife. Much of Belfast remains divided along religious and nationalist lines.

The Orange Order, which organises marches to mark the 1690 victory at the Battle of the Boyne by Protestant Prince William of Orange over Catholic King James of England, was angered this year when authorities ruled they could not walk along a stretch of road that divides the two communities.

That sparked violence on Friday evening, after tens of thousands of Orange Order marchers, wearing orange sashes and waving British flags, paraded at more than a dozen venues across Northern Ireland.

A total 32 police were injured on Friday night in what Chief Constable Matt Baggott described as "shocking and disgraceful" violence, including head, eye and leg wounds.

Another 400 reinforcements were being brought in from Britain as trouble continued through the weekend. More than 20 people have been arrested.