An ex-Royal Navy submarine captain has warned the current situation is "bleak" for anyone aboard the missing Titan submersible and the search-and-rescue operation is quickly turning into a salvage mission.
Ryan Ramsey spoke out as oxygen on the vessel was thought to have run out as of this morning.
Mr Ramsey said: "The outlook is bleak, that's the only word for it, as this tragic event unfolds and almost the closing stages of where this changes from rescue to a salvage mission.
"That doesn't mean to say that the current ships and forces deployed won't continue to keep looking," the submarine expert continued.
"They won't stop for many days, I imagine, but the reality is if you base it off oxygen alone, then they're out of oxygen. Carbon dioxide is also a critical element to it as well as the cold. It would be a miracle if there were survivors from it."
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Rescue efforts have intensified for the lost submersible between Wednesday and Thursday, as the situation is thought to be critical.
Early Wednesday, a Canadian aircraft said it picked up a banging-like noise coming from the vicinity of the sub's last known location, but search efforts in that area turned up nothing.
Aboard the Titan is CEO and founder of OceanGate Expeditions Stockton Rush, British billionaire explorer Hamish Harding, renowned French diver Paul-Henri Nargeolet and Pakistani businessman Shahzada Dawood and his 19-year-old son Suleman Dawood.
The submersible went missing about an hour and a half into its dive on Sunday morning, and an alarm was raised eight hours later - after the vessel missed its surfacing time.
An old video tour of Titan showed that the five passengers currently lost at sea are dealing with cramped conditions and low oxygen during their 5-day ordeal - if they haven't already run out of oxygen, been crushed by pressure, or succumb to extreme cold.
The tiny vessel has no seats, one tiny bathroom, and was navigated using a "video game controller."
CEO of OceanGate Stockton Rush has previously stated in an interview that there may be technical issues with the submersibles.
“We get a lot of challenges …on communications, and just the way we operate is just different than most deep-sea systems. We send odd messages and odd times, and we need them to be received all the time… [We are] working on those challenges."
"There is no shortage of challenges. Had I only known how hard it would be - when you look back, it's just barriers to entry now, at the time, they were barriers to success," Stockton told his interviewers as they all chuckled.
