An expert has shared some of the health risks that passengers on the missing submersible will be facing.
The craft, which is named Titan, went missing earlier this week.
And OceanGate, the company who runs the dive, confirmed that five passengers were on board the sub.
An international search and rescue effort has since been launched to locate the sub.
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But there are some other health risks facing the passengers.
Now rescuers are racing against the clock before oxygen in the vehicle runs out.
And Dr Ken Ledez has told the BBC that running out of oxygen is not the only threat facing the people on board.
Dr Ledez is a specialist in hyperbaric medicine at Memorial University in St John's, Newfoundland.
He explained there is the problem of the vessel possibly losing electrical power, which would affect the level of oxygen being pumped into the cabin.
Ryan Ramsey, who is a former submarine captain in the Royal Navy, added that there could be a build up of carbon dioxide.
He highlighted that there is no system in the vessel to remove carbon dioxide from the cabin.
Adding: "That for me is the greatest problem of all of them."
There is also the risk of hypothermia, as the temperature on the sea floor at that depth is around 0C. If the submersible has no power, then it cannot generate heat.
If a lack of oxygen and rise of carbon dioxide causes them to pass out, then they will not be able to do anything.
Dr Ledez said: "If they're unconscious, they're not going to be able to do much to help themselves."
He added: "If anybody can survive in it, you know, it's these individuals. It just depends on them having power and depends on them having light to be able to find things and make these controls, but absolutely, they could still be alive."
CBS reporter, David Pogue, reported that among the paperwork shown to potential passengers was a waiver which said: "This experimental vessel has not been approved or certified by any regulatory body, and could result in physical injury, emotional trauma, or death."
Rescuers are still searching for the missing vessel after knocking sounds were reportedly heard in the region where it went missing.
Kit Roberts