A Titanic Memorial Garden – with the names of 1,512 victims etched on five bronze plaques – is being opened close to where the liner was launched.
A service is being held in Southampton where the voyage to New York began.
And at the North Atlantic site of the sinking, memorial cruise ship Balmoral is marking the time Titanic hit an iceberg.
Balmoral has arrived at the site where the Titanic sank 400 services miles (460 km) off the coast of Newfoundland on 15 April and passengers and crew are holding commemorations to mark the tragedy.
Another cruise ship, Azamara Journey, has sailed from New York to take part in the ceremony.
Descendants of the victims are expected at the services, and will lay wreaths and join in a minute’s silence in memory of all those who died.
The sinking is also being remembered in other parts of the globe.
Titanic exhibitions are being hosted in Las Vegas, San Diego, Houston and Singapore.
The world’s largest visitor centre opened two weeks ago in Belfast on the Harland and Wolff slipway where Titanic was built. The $153 million building has already attracted more than 45,000 visitors.
In nearby Belfast city centre, the Titanic Memorial Garden was completed this weekend, just in time for the 100th anniversary.
There is no distinction on the memorial between first class passengers and others on board. The names of the dead are simply listed in alphabetical order.
Intriguingly, two of the names have an asterisk beside them – Mr. Thomas Hart and Mr. John Horgan.
Kelly Frizell from Belfast City Council said: “The asterisk means that somebody was travelling under this passenger’s name, but they weren’t the actual passenger in question.
“Whether it’s their true identity or not, a life is a life, and they lost their life.
“There’s no other way to recognize them.
“We couldn’t have left them off.”
Then real identities of Thomas Hart and John Horgan remain a Titanic mystery.
Kelly Frizell spent almost a year researching the victims.
She said: “This is the first monument with all 1,512 names listed in alphabetical order, so it’s very significant.
“It’s breathtaking looking at such a loss. It’s emotional just looking at it.”
The plinth bearing the names is nine metres long. The flowers in the garden were chosen carefully.
Landscape architect Joy Hutchinson said: “We went for a color scheme built around blue, white, silver and green, reflecting water and ice.
“It’s to try to encourage a sense of peace and contemplation.”
In the past two decades, Titanic has become an internationally recognized brand with movies, memorabilia and commercial ventures springing up in different parts of the world.
However, the 100th anniversary is being marked with a series of solemn events, which recognize the tragic reality of the most famous maritime disaster in history.
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