Five people on a tourist submersible bound for the century-old wreckage of the Titanic were confirmed dead on Thursday after a multinational five-day search ended with the discovery of the vessel's debris from a "catastrophic implosion," the U.S. Coast Guard said.

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 meters from the bow of the Titanic, 4 kilometers beneath the surface, in a remote corner of the North Atlantic, U.S. Coast Guard Rear Admiral John Mauger told reporters.

The Titan, operated by the U.S.-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.

The search had grown increasingly desperate on Thursday, when the submersible's estimated 96-hour air supply had been expected to run out if the Titan was still intact, a countdown that proved irrelevant.

The debris' findings matched previous reports about an acoustic signature "consistent with an implosion," which could have resulted from a flood or a failure of the pressure vessel, submarine expert Eric Fusil from the University of Adelaide told ABC News Breakfast.

The submersible, designed to carry up to five people to a depth of 4 kilometers, was subjected to more than 5,500 pounds per square inch (PSI) of pressure when it was at a depth of over 3.2 kilometers, Dr Nicolai Roterman, a deep-sea ecologist and lecturer in marine biology at the University of Portsmouth, told news website Forbes.com.

"If there was any kind of hull breach, the occupants would succumb to the ocean in a near instant," Roterman added.

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.

Here is a timeline of the events beginning from the submersible's descent to the discovery of its wreckage.

(With input from agencies)

(Cover: The undated handout photo shows Titan, the submersible that vanished on an expedition to the Titanic wreckage. /CFP)