Who is Hamish Harding? The British adventurer missing on the Titanic submarine.

British billionaire Hamish Harding has been identified as one of the passengers on board the missing submarine that was diving to the wreck of the Titanic, his family have said.

The 58-year-old chairman of aircraft firm Action Aviation is a renowned adventurer who has flown to space and holds three Guinness World Records. 

He and his wife, Linda, have two sons, Rory and Giles, as well as a stepdaughter, Lauren, and a stepson, Brian Szasz.

Submarine CEO Stockton Rush and French mariner Paul-Henri Nargeolet have also been named as passengers on board. Rush is the chief executive and founder of OceanGate Inc, the company involved in the incident. Nargeolet is the director of the Underwater Research Program at Premier Exhibitions, RMS Titanic.

Read more: A submarine taking people to see the Titanic wreck has gone missing. Here's what we know.

In a now-deleted Facebook post, Szasz said Harding had "gone missing on submarine" and asked for "thoughts and prayers".

The stepson subsequently removed the post, citing respect for the family's privacy.

Over the weekend, Harding said on social media that a ship had set off from the city of St John's, in Newfoundland, Canada, for the destination of the Titanic wreck.

The first dive was set for Sunday morning, according to Harding's post.

"Due to the worst winter in Newfoundland in 40 years, this mission is likely to be the first and only manned mission to the Titanic in 2023," he wrote. 

"A weather window has just opened up and we are going to attempt a dive tomorrow."

There have been no further posts from him.

US and Canadian authorities have launched a search-and-rescue operation, including aerial and surface searches, according to the coast guard and Canada's defence ministry.

OceanGate Expeditions, which operates the submarine, said they were "mobilising all options" to rescue those on the vessel.

"Our entire focus is on the crewmembers in the submersible and their families," they said in a statement on social media. 

"We are deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to re-establish contact with the submersible."

The US Coast Guard said earlier on Twitter a boat on the surface, the Polar Prince, lost contact with the submarine, called the Titan, about one hour and 45 minutes after it began diving toward the site of the Titanic's wreckage on Sunday morning.

In order to visit the wreck, passengers climb inside Titan, which takes about two hours to descend approximately 3,800 metres to the Titanic, which infamously sunk on its maiden voyage in 1912, killing more than 1500 people.

The expedition company said that the craft has life support for its standard load of five people for 96 hours.

Harding is a holder of three Guinness World Records for the longest duration at full ocean depth by a crewed vessel, the longest distance traversed at full ocean depth by a crewed vessel and the fastest circumnavigation via both poles by aeroplane.

Two of these feats were achieved by Harding and ocean explorer Victor Vescovo when they dived to the lowest depth of the Mariana Trench – the deepest part of the ocean – in a two-person deep-submergence vehicle in March 2021.

In June last year, Harding travelled to space with fellow billionaire Jeff Bezos' Blue Origin company. 

He was also part of a team that achieved the fastest circumnavigation of Earth via both geographic poles by plane with a time of 46 hours, 40 minutes and 22 seconds, in 2019. 

– with AAP.

Feature image: Getty.

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