Expedition company OceanGate, the operator of the missing submersible, said that it believed all passengers and the pilot aboard the sub are presumed to be dead, as the U.S. Coast Guard announced that the debris found near Titanic wreckage site were consistent with that of Titan.

"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," OceanGate said in a statement.

OceanGate Expeditions said its pilot and chief executive Stockton Rush – along with U.K. citizens Hamish Harding, Shahzada Dawood and his son Suleman Dawood and French national Paul-Henri Nargeolet "have sadly been lost."

The coast guard said the missing submersible imploded near the wreckage of the Titanic after suffering a "catastrophic loss" of pressure.

"Upon this determination, we immediately notified the families," Rear Admiral John Mauger told reporters in Boston.

"On behalf of the United States Coast Guard and the entire unified command, I offer my deepest condolences to the families."

The five people aboard a submersible visiting the wreck of the Titanic died beneath two miles of ocean after a "debris field" matching the missing submersible was discovered by a robotic deep-sea vessel.

The Coast Guard said five "major pieces" of debris from the Titan submersible have been recovered.

They include part of the pressure chamber, the nose cone, the front-end bell and the aft-end bell.

A remotely operated vehicle (ROV) found debris fields on the North Atlantic Ocean sea floor around 1,600 feet (490 meters) from the bow of the Titanic on Thursday morning.

Undersea expert Paul Hankin said: "We found five different major pieces of debris that told us that it was the remains of the Titan.

"The initial thing we found was the nose cone outside the pressure hull.

"We then found a large debris field.

"Within that large debris field we found the front-end bell of the pressure hull. That was the first indication that there was a catastrophic event.

"Shortly thereafter we found a second smaller debris field. Within that debris field we found the other end of the pressure hull - the aft end bell - which basically comprises the totality of that pressure vessel.

"We continue to map out the debris field, and as the admiral said, we will do the best we can to fully map out what's down there."

The Coast Guard said the ROV that made the discovery was from the Canadian Horizon Arctic ship.