A tourist submarine that takes people to see the Titanic shipwreck went missing in the Atlantic Ocean on Monday, according to the Boston Coastguard.
The US Coast Guard said five people were missing aboard the sub and a search and rescue mission is underway to locate it.
Canada's Coast Guard also joined the search operation, deploying a military aircraft and a ship to assist. The operation was, however, led by the Boston Coastguard who said that the sub was technically lost in their waters.
"We are deploying all available assets to make sure that we can locate the craft and rescue the people on board," said US Coast Guard Rear Admiral John Mauger on Monday.
OceanGate Expeditions, a private company that takes people on expeditions to the Titanic, confirmed that the missing sub was one of theirs in a statement on Monday. The sub, named the Titan, failed to make contact with its tugboat shortly after submerging.
"We are exploring and mobilizing all options to bring the crew back safely," said the statement. "Our entire focus is on the crewmembers in the submersible and their families. We are working toward the safe return of the crewmembers.
"We are deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to reestablish contact with the submersible."
One of the people confirmed to have been on the submarine by his family with British billionaire Hamish Harding. He had posted on Facebook that he was going to board the craft, and his stepson posted on Monday that his stepfather had indeed been on when it went missing.
The second and third passengers confirmed to have been on the sub are Pakistani businessman Shahzada Dawood and his son Suleman, according to the family.
Unconfirmed reports claimed that the fourth passenger was a French diver, while the fifth missing person is reportedly founder and CEO of OceanGate Stockton Rush.
OceanGate charges $250,000 per person for its eight-day expeditions to see the shipwreck, and the sub seats five people, meaning it was full when it went missing. The vessel has the capacity to be underwater for 96 hours which started on Sunday evening when it didn't submerge at the scheduled time.
What is the Titanic?
The Titanic is one of the most famous sunken ships in history, sinking in 1912 on its maiden voyage from the United Kingdom to the United States.
The ship, which was advertised as the "unsinkable ship" struck an iceberg in the Atlantic Ocean and sank, killing 1,500 passengers on board.
The ship was then found almost 40 years ago 4,000 meters under the sea in the Atlantic.