OceanGate, which owned the Titan submarine, said on Thursday it believed the five passengers aboard "sadly lost their lives".
"We now believe that our CEO Stockton Rush, Shahzada Dawood and his son Suleman Dawood, Hamish Harding and Paul-Henri Nargeolet, are sadly missing," the company said in a statement.
"These people were true explorers who shared a special spirit of adventure and a deep passion for exploring and protecting the world's oceans," the statement said. "Our hearts go out to these five souls and every member of their families during this tragic time. We mourn the loss of life and the joy they brought to all they knew," OceanGate said in a statement.
The company added: “This is an extremely sad time for our dedicated employees, who are exhausted and deeply saddened by this loss. The entire OceanGate family is deeply grateful to the countless men and women from numerous organizations in the international community who mobilized vast resources and worked so hard on this mission. We appreciate their commitment to finding these five explorers, and their days and nights of hard work in support of our crew and their families. This is a very sad time for the entire explorer community and for each of the family members of those lost at sea. We respectfully request that the privacy of these families be respected in this most painful time".
What caused the disaster was a "catastrophic loss of pressure", according to the US Coast Guard.
Admiral John Mauge of the US Coast Guard told a news conference that search teams discovered "five different large pieces of debris" identified by the Titan submarine.
The nose cone, located outside the pressure body, was the first part found. Next, they found "a large debris field" that had a pressure hull end bell.
The debris is consistent with a "catastrophic explosion" of the ship, said Mauger, commander of the 1st Coast Guard District.
He made the comments after being asked about the prospects for the recovery of the Titan crew members.
"It's an incredibly unforgiving environment down there at the bottom of the sea, and the debris is consistent with a catastrophic ship explosion," Mauger said.
He said he could not confirm whether the US Coast Guard would be able to find the bodies of the five passengers aboard the Titan submarine.
"We will continue to work and search the area down there, but I don't have an answer on the prospects at the moment," he added.