Protestants attacked police, hijacked cars and barricaded roads in many parts of Northern Ireland after British authorities blocked the province's most controversial Orange Order march.

Several hundred Protestants were camped Monday outside Drumcree Anglican church on the outskirts of Portadown, 30 miles southwest of Belfast, where barbed-wire barricades blocked the Protestant fraternal group's annual parade Sunday before it reached the nearby Roman Catholic section, Garvaghy Road.Protestants confronted riot police and British soldiers in several parts of Belfast overnight, and a policeman was hospitalized with a fractured skull in Londonderry.

David Trimble, leader of Northern Ireland's largest Protestant party and newly elected First Minister of the Northern Ireland Assembly, said he had been in touch with British Prime Minister Tony Blair and other officials to seek a way out of the impasse.

"This situation has the capacity to destabilize, and if the situation is not resolved satisfactorily, it could put at risk all the political progress we have achieved," Trimble said Monday.

Hotels reported a significant number of cancellations, which they blamed on the violence, and tourist officials said the damage could be long-lasting.

As darkness fell Sunday, hard-line Protestants fulfilled their threat to stretch police reserves by rioting - unrest they say will continue until Portadown's Orangemen are allowed to parade down their usual route through a Catholic neighborhood.

In Belfast, mobs of men menaced roads in Protestant areas, prompting many residents to stay home out of fear. Some of those who did drive at night were carjacked, their vehicles confiscated to be used as flaming road barricades.

Police armored cars rammed three burning cars off of north Belfast's Crumlin Road, only to watch rioters steal and burn five more cars to again block the road. The pavement was also littered with broken glass and rocks, a sofa and shattered pinball machine.

In south-central Belfast, rioters briefly spilled onto the "golden mile" of upscale shops, bistros and pubs before police chased them back into the working-class Sandy Row neighborhood. Several vehicles were stolen, upended and burned, providing cover for masked youths who tossed gas bombs at police. Security forces responded with sporadic plastic-bullet fire.

Police reported similar scenes in other Protestant public-housing projects and villages across Northern Ireland - a sign of opposition to a peace process that has meant conceding ground to the north's large Catholic minority.

Police arrested four Catholic men and four teenagers on the roof of an Orange hall in Newry, 30 miles south of Belfast, on suspicion of trying to burn it down.

Democratic Unionist Party leader Ian Paisley, the chief opponent of April's peace agreement, arrived at the Orange standoff in Drumcree at 1 a.m. Monday to huge applause.

"This is a battle that has to be won - no ifs, no buts!" Paisley shouted.

He condemned the decision to prevent Orangemen from marching down Garvaghy Road.