Serious rioting erupted on the streets of west Belfast on Tuesday injuring seven police officers as tension mounted before the culmination of Northern Ireland\'s main Protestant marching season, police said. Police fired plastic bullets at around 200 rioters in the Broadway area of Catholic west Belfast. Rioters responded with a hail of bricks and petrol bombs. Police received unconfirmed reports that shots had been fired, but no civilian injuries were reported. The marching season comes to a climax later Tuesday and marks the Battle of the Boyne in 1690 when King William III, a Protestant, defeated the Catholic King James II, whom William had unseated two years earlier. Trouble flared late Monday when Protestants began lighting bonfires, the signal for the start of a day of celebrations during which thousands of \"Orange Order\" men are expected to march. Northern Ireland saw some of its worst sectarian violence in years two weeks ago, focused on a Catholic enclave in east Belfast. The 1998 \"Good Friday\" peace accords largely ended the cycle of sectarian bombings and shootings in the province, part of the United Kingdom, and paved the way for a devolved, power-sharing Northern Irish Assembly. Around 3,500 people were killed in decades of unrest pitting Protestant Loyalists who want the province to remain part of the United Kingdom aginst Catholic Republicans who favour joining the Irish Republic.