NORTH ATLANTIC: All five people, including two Pakistanis, aboard a submersible missing near the wreck of the Titanic died likely in an instant — after their vessel suffered what the US Coast Guard said on Thursday was a “catastrophic implosion” in the ocean depths.

On board were British explorer Hamish Harding, French submarine expert Paul-Henri Nargeolet, Pakistani-British tycoon Shahzada Dawood and his son Suleman, and Stockton Rush, CEO of the sub’s operator OceanGate Expeditions.

The somber announcement ended a multinational search-and-rescue operation that captivated the world since the tiny tourist craft went missing in the North Atlantic four days ago.

Rear Admiral John Mauger told reporters in Boston that analysis showed debris found on the seafloor, 500 metres from the bow of the Titanic, was consistent with the implosion of the sub’s pressure chamber.

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

OceanGate said its “hearts are with these five souls and every member of their families during this tragic time”.

“These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world’s oceans,” it said in a statement.

The Coast Guard announced earlier on Thursday that an underwater robot had discovered a “debris field” in the search area.

Authorities said they later learned the pieces included the sub’s tail cone and front and back ends of its pressure hull.

Mauger said the Coast Guard could not be sure when or why the vessel imploded and declined to be drawn on whether remains of the men would be retrieved.

“This is an incredibly unforgiving environment down there on the seafloor,” he said.

The process of demobilising personnel and vessels from the scene would soon begin, but unmanned robots would continue operations on the seabed for now, Mauger added.

“We’ll collect as much information as we can,” he said.

The US military originally detected the likely implosion of the craft on secret underwater sound monitoring devices shortly after it went missing on Sunday, the Wall Street Journal reported on Thursday.

“The US Navy conducted an analysis of acoustic data and detected an anomaly consistent with an implosion or explosion in the general vicinity of where the Titan submersible was operating when communications were lost,” an unnamed senior Navy official told the Journal.

The small sub named Titan disappeared on Sunday as it descended to the Titanic, which sits nearly four kilometres below the ocean’s surface and 400 miles off the coast of Newfoundland, Canada.

OceanGate Expeditions charged $250,000 for a seat on the sub. In a 2018 lawsuit, its former director of marine operations raised concerns about the “experimental and untested design” of Titan.

Harding was a billionaire and keen explorer with three Guinness Records to his name, while the Dawoods belonged to one of Pakistan’s richest families.

Nargeolet was nicknamed “Mr Titanic” for his frequent dives at the site.

Harding’s family paid tribute to the aviation tycoon in a statement, saying he was a “passionate explorer” as well as a “loving husband and a dedicated father to his two sons”.

“What he achieved in his lifetime was truly remarkable and if we can take any small consolation from this tragedy, it’s that we lost him doing what he loved,” the family said.

The Dawoods’ loved ones also expressed their “profound grief” at their loss in a brief statement.

The British and Pakistani governments expressed their “deepest condolences” to all the men’s families.

The Dawood Family through a Twitter post expressed their “profound grief”.

“Our beloved sons were aboard OceanGate’s Titan submersible that perished underwater,” the post said.

The family stated that they were grateful to the people who were involved in the rescue operations, adding that untiring efforts were a source of strength for them during this time.

“The immense love and support we receive continues to help us to endure this unimaginable loss,” the post said.

The family expressed condolences to the families of the other passengers who were on the submersible.

On Friday, the Dawood Foundation posted a brief statement grieving the loss of Shahzada and Suleman.

Engro Corporation also took to Twitter to offer their condolences to the Dawood family, grieving the “unthinkable loss” of their vice-chairman Shahzada Dawood.

“Our thoughts and prayers are with the Dawood family at this tragic time,” the conglomerate said in the Twitter post.

The government of Pakistan conveyed their “deepest condolences” to the Dawood family and the other passengers onboard the fateful submersible, according to Radio Pakistan.

According to the state broadcaster, Foreign Office Spokesperson Mumtaz Zahra Baloch, in a statement, said they appreciated the multinational efforts carried out over the last several days in search of the vessel.

The 21-foot (6.5-meter) Titan had been due to resurface seven hours after beginning its descent at 8:00am on Sunday.

But the craft lost communication with its mothership less than two hours in.

Ships and planes from the US and Canadian coast guards, as well as a robot sent from France, scoured 10,000 square miles (around 20,000 square kilometres) of surface water — roughly the size of the US state of Massachusetts — for the vessel.

The search honed in on areas where underwater banging noises were detected late on Tuesday and Wednesday. But Mauger said that ultimately the sounds did not appear to have any relation to the site of the debris.