Debris from the missing submersible Titan was found Thursday morning by a remotely operated underwater vehicle following a four-day search. All five people who were in the sub are presumed dead.

"The debris is consistent with the catastrophic loss of the pressure chamber," U.S. Coast Guard Rear Admiral John Mauger said at a press conference Thursday afternoon. "On behalf of the United States Coast Guard and the entire unified command, I offer my deepest condolences to the families."

The submersible went missing more than 600 kilometres off the coast of Newfoundland Sunday morning during a dive to the wreck of the Titanic. Debris was located roughly 500 metres from the wreck and assessed to be from Titan's external body. Officials said the debris was "consistent with implosion in the water column."

"We're going to continue to investigate the site of the debris field," Mauger said from Boston. "This is something that happened in a remote portion of the ocean with people from, you know, several different countries around the world, and so it is a complex case to work through."

The crew aboard the Titan's support ship, the Polar Prince, lost contact with the submersible on Sunday, about an hour and half into its dive. The U.S. Coast Guard was notified , sparking the around-the-clock search effort.

'CATASTROPHIC FAILURE'

Launched from the Canadian ship Horizon Arctic, the remotely operated vehicle (ROV) located two debris fields and at least five major pieces of the sub, including its nose cone and part of its pressure hull. It is believed the Titan imploded under the immense pressure of the deep ocean before the search and rescue operation even began.

Officials said listening devices detected no sounds consistent with such a "catastrophic failure" and that noises detected earlier by a Canadian aircraft were probably unconnected to the missing sub.

"This was a catastrophic implosion of the vessel, which would have generated a significant broadband sound down there that the sonar buoys would have picked up," Mauger explained. "We will begin to demobilize personnel and vessels from the scene over the course of the next 24 hours."

Until that time, a difficult investigation and search for the crew is ongoing.

"This is a incredibly unforgiving environment down there on the seafloor," Mauger said when asked about the chance of finding human remains. "We'll continue to work and continue to search the area down there, but I don't have an answer for prospects at this time."

The debris was discovered by an ROV owned by Massachusetts-based Pelagic Research Services. The first ROV to arrive on the seafloor, the Odysseus 6K is capable of operating up to the extreme depth of 6,000 metres and is equipped with lights, cameras and a pair of robotic arms. The U.S. Coast Guard announced its arrival aboard the Canadian ship Thursday morning. At least one other ROV was participating.

'THESE MEN WERE TRUE EXPLORERS'

OceanGate Expeditions has been running tours and research trips to the sunken British ocean-liner since 2021. The company has carried at least 46 people to the wreck with some paying approximately $300,000 for the experience. Since the Titan's disappearance, details have emerged from a 2018 engineering report alleging issues with the submersible's structure and its ability to withstand the pressure of ocean where the wreck rests at a depth of 3,800 metres.

The Titan was carrying five passengers: Hamish Harding, a billionaire and explorer; Paul-Henry (PH) Nargeolet, a French explorer; Shahzada Dawood and his son, Suleman, members of a prominent Pakistani family; and OceanGate CEO and Titan pilot Stockton Rush.

"These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world’s oceans," OceanGate said in a statement to Â鶹´«Ã½. "This is an extremely sad time for our dedicated employees who are exhausted and grieving deeply over this loss."

There likely would have been no time to use backup systems that could return the Titan to the surface in an emergency. Even if it hadn't imploded, the oxygen supply on the missing submersible would have passed the estimated maximum 96-hour mark Thursday morning.

Submersibles like the Titan are deployed from a mother ship, while submarines can travel to and from ports under their own power. Although submersibles can be tethered to a ship on the surface, the Titan travelled independently.

'OUTPOURING OF SUPPORT'

As of Thursday afternoon, at least nine vessels remained on the scene. The international air and sea search featured a significant Canadian contribution, with St. John's, N.L. proving to be an important staging ground for the operation.

"The outpouring of support in this highly complex search operation has been robust and immensely appreciated," Mauger from the U.S. Coast Guard said. "We're also incredibly grateful for the full spectrum of international assistance that's been provided."

Canadian assets that participated included Canadian Coast Guard Ships (CCGS) John Cabot, Ann Harvey and Terry Fox. They were joined Thursday morning by the Royal Canadian Navy's HMCS Glace Bay, which carried a mobile decompression chamber and medical personnel in the event the crew were found. A submarine-detecting Royal Canadian Air Force CP-140 Aurora aircraft also assisted.

"Our Canadian partners have been providing critical leadership and significant response capabilities since the beginning of our efforts," Capt. Jamie Frederick of the U.S. Coast Guard told reporters during a press conference in Boston on Wednesday.

With files from CNN and The Associated Press