The US coastguard has indicated those on board the missing submersible that lost contact near the wreck of the Titanic may have no more than a couple of days at best before its life support systems fail.

The submersible craft, Titan, went missing on Sunday in the Atlantic Ocean some 435 miles (700km) south of Newfoundland, Canada.

It is understood from the vessel’s operator, OceanGate Expeditions, Titan has a 96-hour oxygen supply in case of emergencies meaning only around two days of “life support” remain.

A ‘challenging’ search

The US Coast Guard said the 21ft vessel has five people on board, including UK billionaire Hamish Harding, and warned that the search has been “challenging” due to the remote location.

Rear Admiral John Mauger, commander of the First Coast Guard District, said: “It is a remote area and it is a challenge to conduct a search in that area” but added, “we’re deploying all available assets”.

He said the search consists of both looking at the surface and subsurface. The coastguard said Titan lost contact with research vessel Polar Prince approximately one hour and 45 minutes into the vessel’s dive on Sunday morning.

The US Coast Guard Northeast said The Polar Prince and the 106th Rescue Wing would continue surface searches “throughout the evening”.

OceanGate said in a statement that it was “exploring and mobilising all options” to bring the crew back safely.

Sky News also understands that alongside Mr Harding, French submersible pilot, Paul-Henry Nargeolet, and chief executive and founder of OceanGate Expeditions, Stockton Rush, were also on board.

Read more: What we know about the passengers on board missing Titanic submersible

Depth is ‘major problem’

According to OceanGate, the Titan submersible is capable of diving 13,120ft “with a comfortable safety margin” and would take two hours to descend approximately 12,500ft where the Titanic wreck lies.

The vessel operates by pinging back a message every 15 minutes to signal to those ashore that it is safe, however Sky News understands that those pings have stopped.

Marine operations specialist, Mike Welham, outlined the difficulties in the search operation adding that “very specialised underwater vehicles” would be needed to go to the depths of where the wreck is.

Mr Welham told Sky News: “The biggest problem they’ve got is the depth of water that the Titanic site.

“It’s about 3,800m and you need very specialised underwater vehicles to go down to that depth and they’re not really readily available. So they have a major problem if they have to search and recover this vehicle.