The diving company responsible for the Titanic tour trip, OceanGate, says all passengers aboard Titan, the submersible, are dead.
The company made the announcement in a statement on Thursday evening after debris believed to be from Titan was found near the Titanic by rescue teams.
John Mauger, a US coast guard, also said the submersible with five passengers suffered a “catastrophic implosion” killing everyone on board.
On Sunday morning, Titan began a two-hour descent to see the wreckage of the Titanic at the bottom of the North Atlantic Ocean, nearly 13,000 feet below land, southeast of Newfoundland, Canada.
The eight-day journey conducted by OceanGate Expeditions is priced at $250,000 per person.
About an hour and 45 minutes into its descent, Titan lost contact with the Polar Prince, the mothership.
Search efforts began immediately and hours later, a Canadian P-3 aircraft detected underwater noises in the search area but efforts to trace the source were unsuccessful.
Three vessels, including one that has technology that can detect and map out objects on the seafloor, had earlier arrived to join the search for the missing submersible.
The US Coast Guard (USCG) had said the oxygen supply was expected to run out by 1 pm UK time earlier today.
The estimate was based on the number of hours of oxygen the craft had for the five people on board and the time it submerged (1 pm UK time on Sunday).
However, experts said the projected supply of breathable air had chances of an extension if the passengers had taken measures to conserve oxygen.
As search efforts intensified, the USCG said rescue vessels found on the sea floor “consistent with the catastrophic loss of the pressure chamber” from the Titan.
The tail cone of the submersible was found on the sea floor about 1,600 feet away from the bow of the Titanic and other debris nearby, John Mauger, the First Coast Guard District commander, added.
Confirming fears in a statement, OceanGate said it believes the passengers of the Titanic-bound submersible have “sadly been lost”.
“We now believe that our CEO Stockton Rush, Shahzada Dawood and his son, Suleman Dawood, Hamish Harding, and Paul-Henri Nargeolet, have sadly been lost,” the statement said.
“These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world’s oceans. Our hearts are with these five souls and every member of their families during this tragic time. We grieve the loss of life and joy they brought to everyone they knew.”
The company described the loss as a very sad time for the entire explorer community and asked that the privacy of the affected families “be respected during this most painful time”.