A rescue operation is under way deep in the waters of the Atlantic Ocean in search of a submarine that carries people to view the wreckage of the Titanic.

The Joint Rescue Coordination Centre in Halifax, Nova Scotia, said the vessel was reported overdue on Sunday evening about 435 miles south of St John’s, Newfoundland.

Lieutenant Commander Len Hickey said a Canadian Coast Guard vessel and military aircraft were assisting the search effort, led by the US Coast Guard in Boston.

OceanGate Expeditions confirmed the search for its five-person submersible and said its focus is 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.

“We are working toward the safe return of the crew members.”

Atlantic map
(Alamy/PA)

David Concannon, an adviser to the company, said Oceangate lost contact with the sub on Sunday morning. It had a 96-hour oxygen supply, he said in an email to the Associated Press on Monday afternoon.

“Now 32 hours since sub left surface,” said Mr Concannon, who added he was supposed to be on the dive but could not go due to another client matter. He said officials are working to get a remotely operated vehicle that can reach a depth of 20,000ft to the site as soon as possible.

Action Aviation confirmed that its company chairman, UK businessman Hamish Harding, was one of the tourists on board. The company’s managing director Mark Butler told AP the crew set out on Friday.

“Every attempt is being made for a rescue mission. There is still plenty of time to facilitate a rescue mission, there is equipment on board for survival in this event,” he said. “We’re all hoping and praying he comes back safe and sound.”

Chris Parry, a retired navy rear admiral from the UK, told Sky News the rescue mission is “a very difficult operation”.

“The actual nature of the seabed is very undulating. Titanic herself lies in a trench. There’s lots of debris around. So trying to differentiate with sonar in particular and trying to target the area you want to search in with another submersible is going to be very difficult indeed,” he said.

In 2021, OceanGate Expeditions began what it expected to become an annual voyage to chronicle the deterioration of the ocean liner that struck an iceberg and sank in 1912, killing all but about 700 of the roughly 2,200 passengers and crew.

Since the wreckage was discovered in 1985, it has been slowly succumbing to metal-eating bacteria, and some have predicted it could vanish in decades as holes grow in the hull and sections disintegrate.

In describing its first expedition, OceanGate said that in addition to archaeologists and marine biologists, the expeditions would also include roughly 40 paying tourists who would take turns operating sonar equipment and performing other tasks in the five-person submersible.

The initial group of tourists was funding the expedition by spending between 100,000 and 150,000 US dollars (£78,000 to £117,000) each.

OceanGate’s 2023 expedition was its third to the site of the sunken ocean liner to document its deterioration and sea life.

The trip was scheduled to depart from St John’s, Newfoundland, in early May and finish at the end of June, according to a court document filed by the company in April with a US District Court in Virginia that presides over Titanic matters.

OceanGate hired the Canadian vessel Polar Prince, a medium duty icebreaker formerly operated by the Canadian Coast Guard, to ferry dozens of people and the submersible craft to the North Atlantic wreck site.

The submersible, named Titan, is capable of diving 13,120ft “with a comfortable safety margin”, OceanGate said in its filing with the court.

It weighs 20,000lb in the air, but is ballasted to be neutrally buoyant once it reaches the sea floor, the company said.

The Titan is made of “titanium and filament wound carbon fibre” and has proven to “withstand the enormous pressures of the deep ocean”, OceanGate said.

The firm told the court that Titan’s viewport is “the largest of any deep diving submersible” and its technology provides an “unrivalled view” of the deep ocean.