Violence breaks out in Belfast after Protestant march July 12, 2012 -- Updated 2233 GMT (0633 HKT) Nine officers injured, two people arrested after a parade by the Orange Order in Belfast Pro-Irish and pro-British groups hurled objects as they staged rival demonstrations, police say Riot police used water cannon and plastic bullets to bring the crowd under control Police also say petrol bombs were thrown at officers in Londonderry's Bogside area Belfast, Northern Ireland (CNN) -- Violence flared in mainly Catholic districts of Northern Ireland on Thursday, the main day of the annual Protestant marching season. Police said there was "significant but localized disorder" in Belfast's Ardoyne district after a parade by the Orange Order. The march passed without a major incident, but there was tension between pro-Irish and pro-British groups as they staged rival demonstrations. Both sides hurled stones and other objects, police said. Officers were wounded in an attack from pro-Irish youths throwing petrol bombs, fireworks and bricks. The Police Service of Northern Ireland (PSNI) said the officers' injuries were "not life-threatening." "Police and community representatives continue in their efforts to restore order in the Ardoyne area," the statement said. Nine officers were injured. A large number of petrol bombs have been thrown at police. Two arrests have been made at this stage, although this number is expected to rise in the coming days as police continue with their evidence gathering operation," the statement said. The PSNI also said several vehicles were set on fire and pushed at police lines. Riot police used water cannon and plastic bullets to bring the crowd under control. Sporadic violence continued for several hours. There was also disorder in the Northern Ireland city of Londonderry, or Derry as many residents call it. Police said petrol bombs were thrown at officers in the Bogside area, the scene of the Bloody Sunday killings by British soldiers in 1972. Vehicles were also set alight in Derry, and a public bus was hijacked and burned in Craigavon, County Armagh. Assistant Chief Constable Will Kerr, the officer in charge of the policing operation in Belfast, issued a statement condemning the disturbances. "Unfortunately police are dealing with significant disorder," he said. I am urging all individuals and communities affected to respond to developing events in a calm and responsible manner. Violence has serious and unwanted consequences for us all, and we will robustly investigate all incidents of disorder.