UK billionaire Hamish Harding is one of the people on board a missing tourist submersible used to take people to see the wreck of the Titanic.
Sky News understands two others on board the vessel are French submersible pilot, Paul-Henry Nargeolet, and chief executive and founder of OceanGate Expeditions, Stockton Rush.
Mr Harding’s stepson Brian Szasz, said on Facebook: “Hamish Harding my step father has gone missing on submarine thoughts and prayers.
“My stepdad Hamish Harding has gone missing on a submarine pray for a successful recovery.
“Thoughts and prayers for my stepfather Hamish Harding as his Submarine has gone missing exploring Titanic. Search and rescue mission is underway.”
OceanGate Expeditions, a company that deploys vessels for deep sea expeditions, confirmed that one of its submersibles had gone missing in the Atlantic Ocean and that a search is ongoing.
The company said in a statement that it was exploring options to bring the crew back safely and that it had received help from several government agencies in the process.
Action Aviation, an aviation sales and operations company which Mr Harding is chairman of, said on Twitter on Sunday, that the billionaire was “currently diving” and was part of the Titanic expedition.
Vessel has capacity of five people on board
It is not clear how many people were on board at the time, but the submersible has a capacity of five people – a pilot and four guests.
The vessel operates by pinging back a message every 15 minutes to signal to those ashore that it is safe, however Sky News understands that those pings have not been heard for more than seven hours.
The main difference between a submersible and a submarine, is that the former needs a mother ship that can launch it and recover it, while a submarine has enough power to leave port and come back to port under its own power.
Tourists sometimes pay tens of thousands of dollars to be taken to the wreckage of the liner – 12,500ft under water.
OceanGate Expeditions charges $250,000 (£195,270) for a place on its eight-day expedition.
Deep submersible diving is ‘very dangerous’
An explorer has described deep submersible diving as “very dangerous” but added that it is high tech and he is “very hopeful”.
Larry Daley, Newfoundland and Labrador Titanic Explorer said: “Deep submersible diving is very dangerous. But it’s high tech, you know. And each year goes by, the equipment gets better, the technology gets better and so on.
“So I’m very hopeful and very positive. I mean, I was in the sub for 12 hours. We have our own breathing system on board. And if that’s maintained properly, like changing your filter and your Co2 scrubber, you can stay down under for, you know, quite a few hours.
“And in our case, you know, I was down there for 12 hours total time in the sub. And the new technology obviously can extend that too, right.”
The Titanic sank on 15 April 1912 during its maiden voyage from Southampton to New York after hitting an iceberg, with some 1,500 people dying in the disaster.