A single flare was fired above the Harland and Wolff shipyard at 1113 GMT -- exactly a century on from the moment the ill-starred ocean liner, then the largest boat ever built, slid into the waters of Belfast Harbour.
At the time the launch was a moment of huge pride, but ever since the "unsinkable" liner hit an iceberg on its maiden transatlantic voyage nearly a year later the tragedy has hung over Belfast.
The Lord Mayor of Belfast, Niall O Donnghaile, said the centenary should be a moment of celebration for the city, which itself has overcome 30 years of Northern Ireland's sectarian strife known as "The Troubles".
"For too long, Belfast's part in the Titanic story, and the role of the people of Belfast in bringing Titanic to life, has been neglected," O Donnghaile said at the ceremony.
Guests included local schoolchildren and representatives from four other cities and towns linked to the Titanic story -- Cherbourg in France, Cobh in the Republic of Ireland, Liverpool and Southampton.
The Titanic sailed from Southampton and stopped at Cherbourg and Cobh, then known as Queenstown. It was registered in Liverpool, the headquarters of the White Star line, and carried that city's name on its giant stern.
Also present on Tuesday were descendants of many of the men who helped build the ship, some of whom sailed on the first voyage and died in the disaster.
Susie Millar, whose great grandfather Tommy Millar was a deck engineer on board the Titanic and died when the liner sank, said she had mixed feelings.
"Today should be a happy occasion and I was all geared up to be celebratory but when it came to the moment I was actually quite sad," she said.
"You think of what was going through his (her great grandfather's) head 100 years ago.
"He helped to build the ship and would have been part of that team and would've watched the launch and within the next year would've sailed off on her hoping to make a better life for his family and it all went so tragically wrong."
Next year Millar will cross the Atlantic on a specially organised voyage to commemorate the tragedy.
"For me the big clincher there is I get to finish the journey for my great grandfather," she said.
"A hundred years later I get to step off at New York harbour and do what he couldn't do."
The memorial began with a religious ceremony and a moment of silence for the 1,517 passengers and crew who drowned in the disaster.
After the flare was fired, the crowds clapped and cheered for exactly 62 seconds, the length of time it took for the Titanic to roll down the slipway on May 31, 1911.
All boats in the area around the shipyard then sounded their horns in a sign of respect.
An exhibition featuring more than 500 artefacts related to the Titanic, some of them previously unseen, also opened Tuesday at the Ulster Folk and Transport Museum in Northern Ireland.
"No ship has gripped the world's imagination like RMS Titanic. Her remarkable story begins at her birthplace in Belfast," said Niall Gibbons, head of Tourism Ireland, which is involved in the memorial events.
Titanic sank in just over two and a half hours after hitting the iceberg on April 14, 1912.
The last remaining survivor of the sinking, Millvina Dean, died exactly two years ago in England at the age of 97. She was only nine weeks old when the ship went down.