Geraldine McCann carries the Olympic torch towards Parliament Buildings in Belfast June 3, 2012. [Photo/Agencies]

The Olympic torch began its five-day tour of Northern Ireland with plenty of excitement and no signs of trouble Sunday as the territory's Protestants and Catholics vowed to show the world how united the community has become after four decades of conflict.

Police said they had deployed extra security measures to deter the region's small Irish Republican Army factions from trying to disrupt the event. But the Olympic torch proceeded from Belfast's Titanic Quarter to the prosperous belt of towns along the County Down coast with no unusual security evident.

Just as during its first two weeks on British soil in England and Wales, the crowds were free to stand beside the passing torchbearer, who was flanked by four to six tracksuit-clad security staff jogging alongside. Between stops, a Northern Ireland police motorcycle unit well-accustomed to protecting VIPs from terrorist attacks sped ahead, blocking roads on the fly and ensuring that the torch convoy stuck to its ambitious schedule to reach every corner of this province of 1.7 million people by Thursday.

Sinn Fein, the Irish nationalist party that long supported IRA attacks but today helps govern Northern Ireland, said all of Ireland was excited to see the symbol of the 2012 London Games arrive. The flame will cross the border Wednesday into the Republic of Ireland to tour Dublin, a special concession to demonstrate today's exceptionally strong British-Irish relations and cooperation between the two governments on the island of Ireland.

Martin McGuinness, the Sinn Fein deputy leader of the Northern Ireland government and a former IRA commander, said both sides of the community were "exhilarated to be part of an event that's one of the greatest competitions in the world and to be part of a little bit of history."

Sunday's torch run started at dawn in the Belfast docklands where the city's most infamous export, the Titanic, was built a century ago. It headed east to Holywood, best known as the hometown of top-ranked golfer Rory McIlroy, then to the port of Bangor, the major town of a stretch of coastline known as the Gold Coast because of its affluence.

Along the sidewalks, sometimes the crowds of spectators grew to five deep in the hearts of town, but more often the torchbearer was able to wave to single groups of people cheering, whistling, hooting - or occasionally still rubbing sleep out of their eyes, bathrobes on, coffee mugs in hand.

Geraldine McCann carries the London 2012 Olympic torch leg between Newtownards and the Northern Ireland Assembly parliament buildings at Stormont, June 3, 2012. [Photo/Agencies]

The biggest crowd, estimated at 4,000, gathered outside Stormont Parliamentary Building, the home for Northern Ireland's power-sharing government, the cornerstone of the US-brokered peace accord here. Cancer activist Geraldine McCann, 56, received the flame and jogged up the steep slope to the Stormont hilltop with a beaming smile.

After a swing through Belfast Zoo, the torch convoy worked its way past some of the province's most spectacular scenery along the coastal road north past Ireland's best-preserved Norman castle in Carrickfergus, a series of glacier-carved forest glens, and the Giants Causeway, with its strange carpet of hexagonal rocks running down to the Atlantic waves.

As the torch passed through predominantly Protestant towns east of Belfast, the locals' loyalties were on display, with many waving British flags adorned with images of Queen Elizabeth II. Much of the torch's route in coming days goes through predominantly Irish Catholic turf, home to IRA extremists still committed to overthrowing Northern Ireland by force.

Underscoring the threat, a suspected IRA activist tossed a grenade at a police unit Saturday in Northern Ireland's second-largest city, Londonderry, where the Olympic cavalcade will spend parts of Monday and Tuesday.

The police, who were searching a property at the time, weren't injured, but their sports utility vehicle sustained heavy shrapnel damage. Officers arrested a 50-year-old man on suspicion of involvement in IRA activity in a follow-up house raid Sunday.

John Mcalpine carries the Olympic torch in front of Parliament Buildings in Belfast June 3, 2012. [Photo/Agencies]

In Belfast, a police deputy commander, Assistant Chief Constable Alistair Finlay, said the Northern Ireland public would see heavy deployments of officers both along the Olympic torch routes and at events associated with the queen's Diamond Jubilee, also being celebrated this weekend. He said IRA splinter groups "will take any opportunity to cause disruption."

He said people might find roads blocked, and other unexpected security delays. "We are taking these steps to keep communities and their officers safe. We would not do this if it was not absolutely necessary to protect life," Finlay said.

Several spectators said they doubted that any IRA splinter group would seriously disrupt the torch run. They said even if Irish republican extremists tried something, Northern Ireland's people were determined to keep partying anyway.

"We're not going to let that crowd of morons ruin our day. They represent zero-point-zero of the population. This is the real Northern Ireland," said Gareth Wilson, 35, standing with his wife and two sons by the roadside with cell phones in hand, each snapping pictures as the torch cavalcade passed.