During a dive to the Titanic wreck, a journalist who was on board a tourist submersible that is now missing claims that those still inside would be unable to survive on their own.
A significant search and rescue effort was launched after the vessel went missing in the Atlantic Ocean on Sunday.
David Pogue, a CBS correspondent, traveled there last year and documented his experience in a book.
Rescuers would likely have difficulty locating the ship in time, he claimed.
Pogue explained that several bolts that were applied from the outside and required removal by an external crew kept passengers sealed inside the main capsule in his interview with the BBC on Monday.
The craft, which is thought to be OceanGate's Titan submersible, had seven different functions to enable it to resurface, and he said it was "really concerning" that none of them had so far worked.
Pogue claimed that if the sub got stuck or developed a leak, the vessel's resurfacing capabilities wouldn't matter.
There is no backup and no escape pod, he declared. Get to the surface quickly or perish.
According to the US Coast Guard, rescuers are battling against time to find the missing submarine, which typically carries enough oxygen for a crew of five for four days.
The US and Canadian navies, as well as commercial deep-sea companies, are aiding in the rescue effort, according to officials.
Although the rescue effort is being managed from Boston, Massachusetts, the Titanic's wreck is located about 435 miles (700 km) south of St. John's, Newfoundland.
According to his family, the British billionaire entrepreneur and explorer Hamish Harding is on board the submersible.
The fact that GPS and radio don't function underwater further complicates the recovery effort because there is currently "no way" to contact the vessel.
They are able to communicate via short text messages when the support ship is directly above the sub. Those obviously aren't getting a response anymore," Pogue said, noting that Titan had been lost for about three hours on the expedition he was on the previous year.
Because some of the components seemed "off the shelf, sort of improvised," he said he was initially hesitant to board the sub at all.
"You control this sub using an Xbox controller, and some of the ballast is made up of leftover construction pipes. ".
Pogue claimed that Stockton Rush, CEO of OceanGate and the inventor of Titan, had assured him that the carbon-fibre main capsule was "rock solid" and had been created in collaboration with NASA and the University of Washington.
OceanGate claimed in a statement on Monday that the crew members in the submersible and their families were the company's "entire focus.".
The business went on to say that it was "deeply grateful" for the "extensive assistance" that had been provided by government bodies and businesses engaged in deep sea operations.
The Titanic, the biggest ship at the time, collided with an iceberg while making its maiden voyage from Southampton to New York in 1912. More than 1,500 people died out of the 2,200 passengers and crew on board.
Since it was found in 1985, the wreckage has undergone extensive exploration.
