BELFAST (Reuters) - Northern Ireland was hit by a barrage of street violence overnight on the eve of annual parades that often raise tensions between pro-British Protestants and Irish nationalist Catholics in the British region, police said on Thursday.

Vehicles were burned, petrol bombs thrown and roads were closed off in violence in several towns on the eve of July 12 marches to mark the 1690 victory of Protestant King William of Orange over Catholic King James of England.

The annual commemorations, seen as triumphalist by many Catholics, were flash points during 30 years of sectarian violence in the region, in which more than 3,000 people were killed. They have continued to spark low-level street violence since a 1998 peace deal largely ended paramilitary violence.

Protestant youths were angered by a police decision to prevent some traditional bonfires due to a threat to nearby housing.

A blast bomb exploded in the Catholic Short Strand area of Belfast after being thrown from a neighboring Protestant district, police said.

A number of vehicles were hijacked and set on fire in the east of the city and passengers arriving on flights into Belfast City Airport were subjected to a lock-down for over an hour by a suspect bomb in a car abandoned near the entrance. No device was found.

A few miles outside Belfast at Newtownards, County Down, masked men hijacked a bus and set it on fire. Passengers escaped unhurt.

In Londonderry police and fire officers came under petrol bomb and missile attack for a fifth night in a row from Catholic youths in the Bogside area.

Tens of thousands of members of Northern Ireland’s Protestant Orange Order, many in orange sashes and bowler hats, began marching on Thursday to mark King William’s 1690 victory.