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.

Police fired plastic bullets and used water cannon to control crowds of up to 200 people in several Roman Catholic areas of Belfast, a police spokeswoman said. Rioters hijacked a bus and burned a van and motorcycle.

Tens of thousands of Protestants began marches across the province on Tuesday to mark the 1690 victory of King William of Orange over Catholic King James at the Battle of the Boyne, which helped secure Protestant supremacy in Ireland.

Pipe bands and drummers from Scotland joined local groups decked in orange banners and British flags for the marches that Protestant groups say is a central part of their culture, but many Catholics say are provocative.

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

Police appealed for calm and launched major security operations in several sectarian flash points in the city, including the Catholic Ardoyne area, where a march last year sparked three days of rioting.

A sit-down protest by residents early on Tuesday passed off without incident.

"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.

Reuters