The five people aboard a missing submersible died in what appears to have been a "catastrophic implosion," a US coast guard official says, bringing a grim end to the massive international search for the vessel that was lost during a voyage to the Titanic.
A robotic diving vehicle deployed from a Canadian ship discovered a debris field from the submersible Titan on Thursday morning on the seabed some 488 metres from the bow of the Titanic, more than four kilometres beneath the surface, in a remote corner of the North Atlantic, US coast guard Rear Admiral John Mauger told reporters.
The Titan, operated by the US-based company OceanGate Expeditions, had been missing since it lost contact with its surface support ship on Sunday morning about an hour and 45 minutes into what should have been a two-hour dive to the world's most famous shipwreck.
Five major fragments of the 6.7m Titan were located in the debris field left from its disintegration, including the vessel's tail cone and two sections of the pressure hull, coast guard officials said.
No mention was made of whether human remains were sighted.
"The debris field here is consistent with a catastrophic implosion of the vehicle," Mauger said.
The five people aboard included British billionaire and explorer Hamish Harding, 58; Pakistani-born businessman Shahzada Dawood, 48, and his 19-year-old son, Suleman, both British citizens; French oceanographer and Titanic expert Paul-Henri Nargeolet, 77; and Stockton Rush, the US founder and chief executive of OceanGate, who was piloting the submersible.
"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.
"Our hearts are with these five souls and every member of their families during this tragic time."
Rescue teams from several countries had spent days scanning thousands of square kilometres of open seas with planes and ships for any sign of the Titan.
Mauger said it was too early to tell when Titan met its fate but the debris field's position relatively close to the shipwreck and the time frame of the last communication with the Titan seemed to suggest the failure occurred near the end of its descent on Sunday.
The US navy acknowledged an analysis of its acoustic data had detected "an anomaly consistent with an implosion or explosion" near the submersible's location when its communications were lost.
"While not definitive, this information was immediately shared" with commanders of the search mission, a senior navy official said in a statement quoted by the Wall Street Journal.
Citing unnamed US defence officials, the Journal said the sound was picked up by a top-secret system designed to detect enemy submarines.
Filmmaker James Cameron, who directed the Oscar-winning movie Titanic and has ventured to the wreck in submersibles himself, told Reuters he learned of the acoustic findings within a day and knew what it meant.
"I sent emails to everybody I know and said 'we've lost some friends, the sub had imploded - it's on the bottom in pieces right now'," he said.
"I sent that out Monday morning."
Sonar buoys dropped by aircraft had picked up some sounds on Tuesday and Wednesday that temporarily offered hope the Titan was intact and its occupants were alive and trying to communicate by banging on the hull.
But officials said analysis of the sound was inconclusive and the noises probably emanated from something else.
Robotic craft on the ocean floor will continue to gather evidence, Mauger said, but it was not clear whether recovering the victims' remains will be possible given the nature of the accident and extreme conditions at those depths.
The expedition to the Titanic wreck, which OceanGate has been operating since 2021, cost $US250,000 ($A368,000) per person.
Questions about Titan's safety were raised in 2018 during a symposium of submersible industry experts and in a lawsuit by OceanGate's former head of marine operations, which was settled later that year.
© RAW 2023