A major search is underway for a tourism submersible used to explore the Titanic wreck that has gone missing with people on board – including a billionaire explorer.

Five people were reportedly on an expedition when the vessel lost contact less than two hours into the dive in the Atlantic Ocean off south-eastern Canada on Sunday (local time)

The company, OceanGate Expeditions, was operating its fifth Titanic “mission” of 2023, according to its website.

The eight-day adventure costs $US250,000 ($365,100) per person. It starts in Newfoundland, before travelling 640 kilometres to the wreckage site.

Passengers climb inside the 6.7-metre Titan, a five-person submersible, which takes about two hours to descend to the Titanic on the ocean floor.

The truck-sized sub can reach a depth of 4000 metres and usually dives with a four-day supply of oxygen, according to its website.

The US Coast Guard said on Twitter that a boat on the surface, the Polar Prince, lost contact with the submersible about an hour and 45 minutes after it began diving toward the wreckage site on Sunday morning (local time).

US and Canadian authorities have launched a search-and-rescue operation, including aerial and surface searches.

OceanGate Expeditions said in a brief statement it was “mobilising all options” in a search-and-rescue mission.

“Our entire focus is on the crew members in the submersible and their families,” said the statement.

“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.”

It was not immediately clear how many people were missing, but some media were reporting five “crew”, while others said some on board may be tourists.

The submersible usually carries a pilot, three paying guests and a “content expert”.

One of the missing: Hamish Harding buys and sells business jets. Photo: Instagram

Billionaire on board

The family of British billionaire aviation captain Hamish Harding, who has also been to space, said he was on board.

His stepson wrote on Facebook that Mr Harding had “gone missing on  a submarine” and asked for “thoughts and prayers”.

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

Mr Harding, the chairman of Action Aviation business jet brokerage, had posted on Facebook a day earlier he would be aboard the sub.

An adventurer, Mr Harding holds three Guinness World Records.

Two of these feats were achieved by Mr 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.

They spent four hours and 15 minutes traversing the deepest part of the ocean and travelled 4.6 kilometres at that depth.

In July 2019, Mr Harding was 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 June last year, he travelled to space with fellow billionaire Jeff Bezos’ Blue Origin company.

The Titanic passenger ship famously sank in 1912 on its maiden voyage after striking an iceberg, killing more than 1500 people.

The story has been immortalised in non-fiction and fiction books, as well as the 1997 blockbuster movie Titanic.

A photo from a previous OceanGate Expeditions dive. Photo: Instagram

Titanic adventure

An expedition package with OceanGate Expeditions includes one submersible dive, private accommodation, all required training, expedition gear and all meals while on board.

Day one departs from St John’s, Newfoundland, and heads for the wreck site, with guests learning safety information and dive day logistics during the journey, which can take two days.

Diving can start as soon as day three, when final dive checks are undertaken before climbing into the Titan.

“Once the submersible is launched you will begin to see alien-like lifeforms whizz by the viewport as you sink deeper and deeper into the ocean,” the website states.

“The descent takes approximately two hours but it feels like the blink of an eye.

“Soon you will arrive at depth, and after some navigating across the seafloor and debris field, finally see what you’ve been waiting for: The RMS Titanic.

“Enjoy hours of exploring the wreck and debris field before making the two-hour ascent to the surface.”

The expedition steams back to shore on day seven, arriving on day eight back in Newfoundland.