The crew onboard the Titanic submarine, including a 19 year-old Glasgow student are believed to be dead.
The owner and operator of the Titan vessel released a statement saying they believe the five men are "sadly lost".
The craft submerged on Sunday morning before its support vessel lost contact about an hour and 45 minutes into the trip, according to the Coast Guard.
OceanGate's statement read: "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.
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"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.
"This is an extremely sad time for our dedicated employees who are exhausted and grieving deeply over this loss.
"The entire OceanGate family is deeply grateful for the countless men and women from multiple organizations of the international community who expedited wide-ranging resources and have worked so very hard on this mission.
"We appreciate their commitment to finding these five explorers, and their days and nights of tireless 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 ask that the privacy of these families be respected during this most painful time."
Strathclyde business student Sulema Dawood, 19, was among the five onboard along with his dad Shahzada, 48, British billionaire Hamish Harding, "Titanic's greatest explorer" Paul-Henri Nargeolet and CEO of OceanGate Stockton Rush.
