A British billionaire adventurer is among five people on board a submersible that went missing on a dive to the wreck of the Titanic.

Hamish Harding, who runs an aviation company, was on the 21ft vessel when it set off on Sunday morning for what should have been an eight-hour trip to the bottom of the Atlantic.

A rescue mission involving the US Coast Guard and an aircraft that can detect underwater vessels was under way on Monday as rescuers raced to reach the group before their oxygen supplies were exhausted.

The submersible has 96 hours of oxygen, and rescuers warned that it could take up to two days to reach the ocean floor if the craft had sunk there.

The OceanGate Expeditions tour group, which takes keen explorers to the depths of the Atlantic for $250,000 per person, is believed to have lost contact when it was directly above the Titanic.

The Boston Coast Guard said its crew was “searching for an overdue Canadian research submarine approximately 900 miles off Cape Cod”.

The submersible, which launched from Canadian research vessel Polar Prince, “submerged Sunday morning, and the crew of the Polar Prince lost contact with them approximately one hour and 45 minutes into the vessel’s dive”, the Coast Guard said.