Experts fear the five people on board the missing Titanic research vessel won't be found alive.
They say that the oxygen will run out onboard by 12.08pm today. Additional help has been sent to find the missing Titan submersible but so far, it has not been found.
The vessel lost communication with tour operators on Sunday while about 435 miles south of St John's, Newfoundland, during a voyage to the Titanic shipwreck off the coast of Canada. As of Wednesday afternoon, it was thought just 20 hours of oxygen remained.
Richard Garriott de Cayeux, president of The Explorers Club, has confirmed it is sending support to help with the search for the vessel which has British billionaire adventurer and founding member of the Board of Trustees of The Explorers Club Hamish Harding on board, but criticised the time taken to get that help accepted.
READ MORE: Titanic submarine LIVE: search mission updates as hours of oxygen left in submarine
He wrote in a statement published on Twitter: "Thanks for all your support and hard work on the rescue operations for our friends aboard Titan. I believe we have importantly improved the odds of a positive outcome through our advice, volunteering of services and equipment, and even the political pressure we continue to bring to bear.
"All has been needed. All continues to be needed. Magellan is en route (should have been accepted sooner), we are still trying to get side scan sonar (should have been accepted sooner), and still working on ships to transport equipment and other details.
"We continue to come together for our friends, their families and the ideals of The Explorers Club, and the cause of safe scientific exploration of extreme environments. There is good cause for hope and we are making it more hopeful."
The remotely operated vehicle (ROV) provided by Magellan was used last year to scan the Titanic wreckage and can go as deep as 6,000m but reportedly could take up to 48 hours to arrive at the scene. It will be able to provide help in searching for the missing submersible once it arrives at the search area.
The 6.7m (22ft)-long OceanGate Expeditions vessel is said to have had a 96-hour oxygen supply in case of emergencies. As well as Mr Harding, in the undersea craft are UK-based businessman Shahzada Dawood, his son Suleman Dawood, and OceanGate's chief executive and founder Stockton Rush, as well as French submersible pilot Paul-Henri Nargeolet.
The US coast guard has been leading an international rescue effort which was stepped up after underwater noises were heard on Tuesday and again on Wednesday, although experts have been unable to determine the cause of the sound.
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