Rescuers in a remote area of the Atlantic Ocean raced against time early Tuesday to find a missing submersible carrying five people on a mission to document the wreckage of the Titanic.

The carbon-fibre submersible named the Titan, part of a mission by OceanGate Expeditions, carried a pilot, a renowned British adventurer, two members of an iconic Pakistani business family and a Titanic expert. Authorities reported the vessel overdue on Sunday night about 435 miles (700 kilometres) south of St John’s, Newfoundland, according to Canada’s Joint Rescue Coordination Centre.

Every passing minute, however, puts the Titan’s crew at greater risk. The submersible had a 96-hour oxygen supply when it put to sea at roughly 6am on Sunday, according to David Concannon, an adviser to OceanGate.

“It is a remote area – and it is a challenge to conduct a search in that remote area,” said Rear Admiral John Mauger, a commander for the US Coast Guard, which also is searching for the Titan. Mauger told NBC’s “Today” show on Tuesday that his crews were working to prioritise underwater search efforts and get equipment there that can be helpful to the search.

“We’re working very, very hard to make sure that we bring all assets … to bring leading technical experts to understand what capability is available, what capability we can get to the team,” he said.

The Canadian research icebreaker Polar Prince, which was supporting the Titan, reportedly lost contact with the vessel about an hour and 45 minutes after it submerged. The Polar Prince was to continue to do surface searches throughout the night and a Canadian Boeing P-8 Poseidon reconnaissance aircraft will resume their surface and subsurface search in the morning, the US Coast Guard said on Twitter. Two US Lockheed C-130 Hercules aircraft also have conducted overflights.

The Canadian military also dropped sonar buoys to listen for any possible sounds from the Titan.

Ship-tracking satellite data from MarineTraffic.com analysed by The Associated Press showed the Polar Prince some 430 miles (690 kilometres) southeast of St John’s on Tuesday morning. The Bahamas-flagged cable layer Deep Energy was nearby as well, likely assisting in the surface search.

In an earlier email to the AP, Concannon said he was supposed to be on the dive but could not go. He said officials were working to get a remotely operated vehicle that can reach a depth of 3.7 miles (6 kilometres) to the site as soon as possible.

OceanGate’s expeditions to the Titanic wreck site include archaeologists and marine biologists. The company also brings people who pay to come along, known as “mission specialists.” They take turns operating sonar equipment and performing other tasks in the five-person submersible.

The Coast Guard said on Monday that there was one pilot and four “mission specialists” aboard. However, OceanGate’s website suggests that the fifth person aboard may be a so-called “content expert” who guides the paying customers.

OceanGate said its focus was on those aboard 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 reestablish contact with the submersible,” it said in a statement.

Authorities have yet to formally identify those on board, although some names have been confirmed.

British businessman Hamish Harding, who lives in Dubai in the United Arab Emirates, was one of the mission specialists, according to Action Aviation, a company for which Harding serves as chairman. The company’s managing director, Mark Butler, told the AP that the crew set out on Friday.

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

Harding is a billionaire adventurer who holds three Guinness World Records, including the longest duration at full ocean depth by a crewed vessel. 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.

Harding was “looking forward to conducting research” at the Titanic site, said Richard Garriott de Cayeux, the president of The Explorers Club, a group to which Harding belonged.

“We all join in the fervent hope that the submersible is located as quickly as possible,” he said in a statement.

Also on board were Pakistani nationals Shahzada Dawood and his son Suleman, according to a family statement sent to the AP. The Dawoods belong to one of Pakistan’s most prominent families. Their eponymous firm invests across the country in agriculture, industries and the health sector.

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

Shahzada Dawood also is on the board of trustees for the California-based SETI Institute that searches for extraterrestrial intelligence. French explorer and Titanic expert Paul-Henry Nargeolet also was on board, according to David Gallo, a senior adviser for strategic initiatives and special projects at RMS Titanic. Gallo identified Nargeolet, a friend who has led multiple expeditions to the Titanic, on Tuesday during an interview with CNN.

The expedition was OceanGate’s third annual voyage to chronicle the deterioration of Titanic, which struck an iceberg and sank in 1912, killing all but about 700 of the roughly 2,200 passengers and crew. Since the wreckage’s discovery in 1985, it has been slowly succumbing to metal-eating bacteria. Some have predicted the ship could vanish in a matter of decades as holes yawn in the hull and sections disintegrate.

The initial group of tourists in 2021 paid $100,000 to $150,000 apiece to go on the trip. OceanGate’s website had described the “mission support fee” for the 2023 expedition as $250,000 a person.

Unlike submarines that leave and return to port under their own power, submersibles require a ship to launch and recover them. OceanGate hired the Polar Prince to ferry dozens of people and the submersible craft to the North Atlantic wreck site. The submersible would make multiple dives in one expedition.

The expedition was scheduled to depart from St John’s, Newfoundland, in early May and finish up at the end of June, according to documents filed by the company in April with a US District Court in Virginia that oversees Titanic matters. CBS journalist David Pogue, who went on the trip last year, noted his vessel got turned around looking for the Titanic.

“There’s no GPS underwater, so the surface ship is supposed to guide the sub to the shipwreck by sending text messages,” Pogue said in a segment aired on CBS Sunday Morning. “But on this dive, communications somehow broke down. The sub never found the wreck.”

The submersible, named Titan, is capable of diving 2.4 miles (4 kilometres) “with a comfortable safety margin,” OceanGate said in its court filing.

It weighs 20,000 pounds (9,072 kilogrammes) in the air, but is ballasted to be neutrally buoyant once it reaches the seafloor, the company said. 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.

During its expedition in 2022, 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. More missions, however, followed. OceanGate has described the submersible as a “state-of-the-art vessel” that “is lighter, more spacious and more comfortable than any other deep-diving submersible exploring the ocean today.”

But the custom-built, titanium-domed Titan represented a risk. Pogue and another passenger, a writer and producer for the cartoon series “The Simpsons” named Mike Reiss, noted how the liability waiver for the trip included stark safety warnings. Pogue in his CBS piece also highlighted how much of the “improvised” submersible, about the size of a minivan, operated with a single button, a video game-style controller, a makeshift toilet and material from an RV retailer.

Experts said Monday that rescuers face steep challenges.

Alistair Greig, a professor of marine engineering at University College London, said submersibles typically have a drop weight, which is “a mass they can release in the case of an emergency to bring them up to the surface using buoyancy.”

“If there was a power failure and/or communication failure, this might have happened, and the submersible would then be bobbing about on the surface waiting to be found,” Greig said.

Another scenario is a leak in the pressure hull, in which case the prognosis is not good, he said.

“If it has gone down to the seabed and can’t get back up under its own power, options are very limited,” Greig said. “While the submersible might still be intact, if it is beyond the continental shelf, there are very few vessels that can get that deep, and certainly not divers.”

Even if they could go that deep, he doubts they could attach to the hatch of OceanGate’s submersible.

• An AP report