There is now a race against time to find the deep-sea vessel that went missing on Sunday while on a trip down to the Titanic wreckage off the coast of Canada.

The submersible, named Titan, lost communication with tour operators about 435 miles south of St John’s, Newfoundland, and the US Coastguard predicts the vessel will run out of breathable air around 10am GMT on Thursday.

Here’s what we know so far:

– Where are rescue teams searching?

Titan is believed to be around 900 miles east and 400 miles south of Newfoundland. It is unknown how deep the vessel is, with the seabed being around 3,800m from the surface.

Who is involved in the search operation and what equipment are they using?

The US Coast Guard confirmed three boats have arrived at the area where “banging” has been heard by a Canadian P-3 aircraft early on Wednesday.

The John Cabot, Atlantic Merlin and Skandi Vinland were the first to arrive with the following vessels also in the area:

– Canadian CGS Ann Harvey– Canadian CGS Terry Fox– Motor Vessel Horizon Arctic– French Research Vessel L’Atalante (ROV)– His Majesty’s Canadian Ship Glace Bay (a mobile decompression chamber and medical personnel)

The Explorers’ Club said it was ready to provide the UK-based Magellan’s remotely operated vehicle (ROV) that is certified to travel as deep as 6,000m.

Rear Admiral John Mauger of the US Coast Guard told BBC News there is a number of plans should they find Titan, with a range of equipment ready.

He said: “While our unified command is fully focused on the search we have experts that are working those different scenarios and we have mobilised gear on site, we have lift capabilities on the vessels that are on site now we have additional lift capability coming in.

“The (US) Navy has mobilised a submerged object recovery system that they have and the Canadian armed forces have mobilised a recompression chamber with medical support.

“We’re preparing for contingencies while remaining laser-focused on the search for the submersible and those people.”

– What is the scale of the search?

The search area has been compared to the size of Wales, with Dik Barton, the first British man to visit the Titanic wreckage, telling the PA news agency the scale is “huge”.

“We can work out roughly the trajectory of the submersible from the point of release.

“We know what the tides are doing, what the water’s like, the water column and how it behaves, we relatively know well how the local tides and currents work.

“But when this is released and out of communication one hour and 45 minutes later that’s going to put it about the 2,000 metre to 25,000 metre mark, and after that who knows?

“What happens is the vessel goes into a controlled descent.

“If they’ve lost communications that means they’ve probably lost power of some sort and as a consequence of that you’ve lost control. It’s conjecture and you have to be positive and optimistic about these things.”

He added: “You’re working in the dark and an environment which is so restricted because of the size and direction, you literally have no idea where you want to go.”

– Who is onboard Titan?

Titan is carrying five people, including British billionaire adventurer Hamish Harding.

The others are UK-based businessman Shahzada Dawood, his son Suleman Dawood, OceanGate’s chief executive and founder Stockton Rush and, reportedly, French submersible pilot Paul-Henri Nargeolet.

– How long is left to find Titan?

Rear Admiral Mauger estimated earlier on Wednesday there could be only 20 hours of oxygen left inside Titan.

He said: “Based on information that the operator provided, they indicated that they have an emergency life-support system onboard to provide oxygen for approximately 96 hours.

“I understand that is a difficult calculation to predict because it depends on the number of occupants and their consumption but we are looking at a period of time of about 20 hours from now into tomorrow morning that we may be at the end of the 96-hour window.”

He said the prediction was breathable air could last to around 10am GMT.

– What other factors could harm the crew?

Former Royal Navy submarine captain Ryan Ramsey said one problem may also be the levels of carbon dioxide onboard.

He said: “For this particular mission, if they’re on the seabed at the moment they’re 4,000m down. The water temperature for down there is about 0C, they’ve got no electricity so they’re not generating any power which means they can’t generate heat.

“That’s the first element, they’re dealing with the cold, if they’re still there they’ve been there for three days. The second challenge is air.

“Everybody keeps talking about oxygen and how there’s only 20 hours left, maybe they could extend that by slowing down breathing rates but that becomes really difficult considering the stress they will be under in this particularly horrific situation.

“Then the third one, which hasn’t really been talked about, is carbon dioxide. Obviously, when you breathe out you breathe out carbon dioxide and there is nowhere for that carbon dioxide to go.

“When I looked on YouTube at the inside of the Titan there didn’t appear to be any form of carbon dioxide removal system, what are called scrubbers.

“That for me is the greatest problem of all of them.”

– How likely is it Titan can be found before the breathable air runs out?

Mr Ramsey claims it is unlikely the submersible will be found inside the time frame but remains hopeful.

He said: “I would really like to be proven completely wrong and they turn up on the surface, in the next few hours, they’re located, and everything ends well.

“But I think you have to be realistic, and the odds are against them in every single way possible.

“We may never know the outcome of this because they never detect it and so we have to make the assumption that this is not going to end as well as we would like.”