The US Coast Guard has given an update on the 'complex' search for the missing Titanic submersible.
A major operation is underway to locate the OceanGate sub that disappeared on Sunday (18 June).
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The five-person vessel set off over the weekend for its deep sea exploration of the Titanic wreck, which is some two miles or so beneath the Atlantic Ocean.
But as the tiny vessel made its descent, it suddenly vanished, with no way of knowing as yet where it went.
On board are five crew members: British billionaire Hamish Harding; Shahzada Dawood and his son Sulaiman; French maritime expert Paul-Henri Nargeolet; and OceanGate CEO Stockton Rush.
Each of them had to pay around $250,000 to be part of the crew heading down to the wreckage.
In an update on the search and rescue mission, the US Coast Guard confirmed that 'to date, search efforts have not yielded any results'.
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Speaking about the operation, Captain Jamie Frederick, of the First Coast Guard District, said it was 'complex' and 'requires multiple agencies'.
He explained that the Titan vessel now had just 40 hours of oxygen left for the five passengers, with the sub able to remain underwater for 96 hours.
Since the rescue mission began, the Coast Guard and other services have been searching an incredible '7,600 square miles, an area larger than state of Connecticut'.
UK businessman Harding has taken part in a number of expeditions in the past, visiting Challenger Deep, the deepest point of the ocean, as well as going on the Blue Origin space mission.
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Retired astronaut Colonel Terry Virts today (20 June) revealed the final text message that Harding sent to him before he set off on his Titan journey.
Speaking to Good Morning Britain, he said: "We don't really talk about risks, it's known. He understood the risks for sure, there's no doubt about that.
"The last text I got was, 'Hey, we're headed out tomorrow, it looks good, the weather's been bad so they've been waiting for this'."
"He went down to the deepest part of the ocean, set a few world records at the Mariana Trench and we talked quite a bit about the risks and the different things that they were going to be able to do. So he was very excited about it."
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Harding is the chair of Action Aviation Group, a company which brokers the sales of aircraft including airliners and 'business jets'.
A statement from Harding on the company's website lists their clients as including 'Fortune 100 companies, international corporations, heads of state, families and VIPs from the sports, entertainment industries'.
Featured Image Credit: Twitter/Reuters/OceanGateTopics: US News