Rescue teams are in a race against time to find a submersible tourist vessel which went missing during a voyage to the Titanic shipwreck off the coast of Canada, with a British billionaire among five people aboard.

There may be as little as 56 hours of emergency oxygen left aboard the submersible, named Titan, which lost communication with tour operators on Sunday while about 435 miles south of St John’s, Newfoundland.

Private plane firm Action Aviation said its British chairman Hamish Harding is one of the mission specialists on the five-person OceanGate Expeditions vessel, which is 6.7 metres long (22ft).

UK-based businessman Shahzada Dawood and his son Sulaiman have also been named in a family statement as two of the other people on board the “very tiny” craft.

They belong to one of Pakistan’s most prominent families and their firm, the Dawood Hercules Corporation, invests across the country in agriculture, industries and the health sector.

French submersible pilot Paul-Henry Nargeolet and chief executive and founder of OceanGate Expeditions Stockton Rush are also on the vessel, according to reports.

The US Coast Guard is leading search efforts and Rear Admiral John W Mauger estimated there was 70 to 96 hours left to find them at a press conference held just before 5pm Boston time (10pm BST) on Monday.

A statement from the Dawood family obtained by CNN, said: “As of now, contact has been lost with their submersible craft and there is limited information available.

“We are very grateful for the concern being shown by our colleagues and friends and would like to request everyone to pray for their safety while granting the family privacy at this time.

“The family is well looked after and are praying to Allah for the safe return of their family members.”

Shahzada Dawood is vice-chairman of Pakistani conglomerate Engro Corporation, which was founded as a fertiliser business, and an adviser to the King’s charity, Prince’s Trust International.

The charity’s chief executive Will Straw said: “Prince’s Trust International has a longstanding relationship with Shahzada Dawood and his family.

“We are shocked by this awful news, praying for a rescue and sending our thoughts to his family during this deeply challenging time”.

It is understood the Dawood family, who live in Surbiton, south-west London, are in Canada for a month.

The search and rescue operation, involving military aircraft 900 miles east of Cape Cod, was continuing on Tuesday.

The US Coast Guard said the Canadian research vessel Polar Prince and 106 Rescue wing will continue to conduct surface searches alongside two US C-130 flights.

Oceanologist Dr Simon Boxall, of the University of Southampton, said a distress signal from the submersible was sent out.

He told the PA news agency: “This is second-hand knowledge but my understanding is that they have received a signal from the submarine.

“You can’t use radios underwater. You rely totally on ‘pings’. What they have is really limited communication.

“Apparently they have had, and I don’t know when… they have had an emergency ping saying the vessel is in distress. I don’t know if that is automatically generated or generated by people on board,” he said, adding he did not know when the message was transmitted.

Dr Boxall said rescuers would have to first locate the submarine which is not a “trivial ask” as it could be as much as 4km (2.5 miles) deep, while the boat is beyond the reach of helicopters.

Very few vessels can reach the sort of depths that may be needed to carry out a successful rescue mission, he told GB News.

Mr Harding holds three Guinness World Records, including the longest duration at full ocean depth by a crewed vessel when, in March 2021, he and ocean explorer Victor Vescovo dived to the lowest depth of the Mariana Trench. In June 2022, he went into space on Blue Origin’s New Shepard rocket.

On social media at the weekend, he said he was “proud to finally announce” he would be aboard the mission to the wreck of the Titanic, the luxury ocean liner which hit an iceberg and sank in 1912, killing more than 1,500 people.

Tour operator White Desert Antarctica, with whom Mr Harding has travelled, said all at the company are “praying” that those missing are found safe and well.

Founder Patrick Woodhead said: “We have faith in the incredible emergency services now focused on finding the sub in the area around the Titanic. Hamish has been a true friend to White Desert for many years and is an incredible aviation explorer in his own right.”

OceanGate Expeditions said its focus was on those aboard the vessel and their families.

“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 company said in a statement.

The Titan vessel weighs 10,432kg (23,000lbs) and is capable of diving to depths of 4,000m (13,120ft) “with a comfortable safety margin”, according to operator OceanGate.

In a May 2021 court filing, OceanGate said the Titan had an “unparalleled safety feature” that assesses the integrity of the hull throughout every dive.

At the time of the filing, Titan had undergone more than 50 test dives, including to the equivalent depth of the Titanic, in deep waters off the Bahamas and in a pressure chamber, the company said.

During its 2022 expedition, OceanGate reported that the submersible had a battery issue on its first dive and had to be manually attached to its lifting platform, according to a November court filing.

CBS journalist David Pogue, who went on the trip last year, said the liability waiver included stark safety warnings.

The submersible was taking part in OceanGate’s third annual voyage to monitor the decay of the ship’s wreckage, following expeditions in 2021 and 2022.

The cost of the 2023 expedition is 250,000 dollars (£195,957) per person, as stated on the OceanGate’s website.