This combination of pictures created on June 21, 2023 shows Titan submersible passengers (L-R, top to bottom) Hamish Harding, Stockton Rush, Paul-Henri Nargeolet, Suleman Dawood and his father Shahzada Dawood. Photo: Handout, Joël SAGET / AFP / Dirty Dozen Productions / OceanGate Expeditions / DAWOOD HERCULES CORPORATION
Efforts to locate the missing tourist submersible near the wreck of the Titanic in the North Atlantic are entering a critical phase.
Salvage work must start within hours as the oxygen supply of the five men on board is running out.
The US Coastguard has doubled the search area, and a French ship with a robot that can reach the seabed nearly four kilometres down is on site to assist search and rescue efforts.
Rescuers are racing against the clock, with oxygen estimated to run out about 11pm New Zealand time.
Ten ships and several remote subs have joined the hunt for the missing sub that was off to view the wreckage of the Titanic on Monday.
It lost signal with its mothership and more than three days later, its location remains unknown,
Prof Alistair Greig from University College London told the BBC that if the Titan was found trapped in wreckage on the sea bed it would normally take two hours for it to rise to the surface under its natural buoyancy once it had been released.
"Every step takes time and time is what we are running out of."
On board are British adventurer Hamish Harding; Shahzada and Suleman Dawood, a father and his 19-year-old son from a prominent Pakistani business family; Titanic expert and former French Navy diver Paul-Henry Nargeolet and Stockton Rush, the CEO of OceanGate, the company that operates the sub.
Photo: AFP / OceanGate Expeditions
A French deep-sea robot has been deployed to the area where banging sounds have been heard, but whether the noises are signs of life is inconclusive.
The vessel can only be opened from the outside and is likely 4km deep, where temperatures are at hypothermic levels and the water pressure is intense.
An American oceanographer believes rescuers hunting for the submarine need to head immediately to the area where banging has been heard.
David Gallo, who helped to create the first map of the Titanic wreck, says even if the vessel is found soon, it will take hours to winch up.
He told Checkpoint that rescuers need to take a chance on the noises.
"Now that they know there are sounds that it could be the submarine, they need to assume that it is because we're out of time, and start sending the right kind of equipment to that spot.
"In case it really is the sub, you're there already. You don't have to wait for other equipment to come over, and get in the water."
Gallo said French dive expert Paul Henry Nargeolet, who is on board the Titan, would know to make noises in the hope they would be detected.
Gallo also told CNN, "It's going to be almost impossible. We need a miracle - but miracles do happen."
A retired US Navy submarine captain has told CNN that if alive, the people on board the Titan will be very uncomfortable.
Captain David Marquet said they will be freezing cold from the waters around the vessel.
They will see their breath; there is likely to be frost on the inside of the submarine and they would be huddling together to conserve body heat.
Experts also say the cold environment will depress body functions and decrease the air needed.
A friend of one of the men on board, Chris Brown, pulled out of the trip due to safety concerns.
He said OceanGate did not want to become certified for one trip let alone multiple. He also raised concern about the materials used, saying they were "off the shelf".
Will Kohnen from the Marine Technology Society told CNN there are 10 submarines in the world that can go to 3.5km and deeper. All of them are certified except the OceanGate submersible.
A German businessman who was one of OceanGate's first customers for diving to the Titanic said it was like a "kamikaze operation".
Arthur Loibl told AP people had to be a little crazy to do it.
- RNZ