BOSTON (NewsNation) — The five people onboard a missing submersible that was headed for the Titanic shipwreck on Sunday have approximately “40 hours of breathable air left,” the U.S. Coast Guard estimated Tuesday afternoon.

So far, search and rescue teams have been unable to find the vessel, which is believed to be about 900 miles east of Cape Cod, Massachusetts.

“You’re dealing with a surface search and a subsurface search and frankly that makes it an incredibly complex operation,” Capt. Jamie Frederick with the First Coast Guard District said at a news conference Tuesday.

Now, rescuers are in a serious race against time. As of 1 p.m. Eastern Tuesday, the five people in the sub have about 40 hours before they run out of air.

Late Tuesday night, the U.S. Coast Guard said “underwater noises” were detected by a Canadian P-3 aircraft. Remotely-operated vehicles were relocated to investigate, but nothing was found.

Finding the sub is just part of the challenge. Officials will also have to figure out how to recover the vessel, which could be as far as two miles underwater.

“If the sub is located, then the experts need to look at what is the best course of action for recovering the sub,” said Frederick. “But I think it’s going to depend on that particular situation and if we encounter that.”

The U.S. Navy is sending a lift system that’s designed to recover “large, bulky, and heavy undersea” objects, a spokesperson told NewsNation. That equipment is scheduled to arrive in St. John’s, Newfoundland on Tuesday evening.

A Canadian P3 aircraft arrived at the scene Tuesday to conduct sonar searches, according to the First Coast Guard District. So far, crews have searched 10,000 square miles — an area larger than the state of Connecticut — the Coast Guard said Tuesday night.

A C-130 crew from the U.S. Air National Guard also arrived Tuesday afternoon to continue searching.

A slew of other vessels are also en route to the scene, the Coast Guard said. They include:

• Canadian CGS John Cabot
• Canadian CGS Ann Harvey
• Canadian CGS Terry Fox
• Canadian CGS Atlantic Merlin (remotely operated vehicle) 
• Motor Vessel Horizon Arctic 
• Commercial Vessel Skandi Vinland (remotely operated vehicle) 
• French Research Vessel L’Atalante (remotely operated vehicle) 
• His Majesty’s Canadian Ship Glace Bay (mobile decompression chamber and medical personnel) 

As of Monday night, authorities would not confirm the identity of anyone aboard.

The missing sub called Titan, which holds up to five people onboard, carries tourists to view the Titanic’s remains about 12,000 feet at the bottom of the Atlantic Ocean off the coast of Newfoundland, Canada. The infamous ship sank in 1912 after hitting an iceberg.

The crew began its two-mile underwater descent to see the wreckage from the Titanic early Sunday morning. But an hour and 45 minutes into its voyage, the vessel stopped communicating.

The sub has no GPS or locator beacon, but it’s capable of floating to the ocean surface on its own.

It is unclear whether the tour had gotten lost or if there was an issue on board. There are concerns the Titan may have suffered a catastrophic failure underwater.

But by air and by sea, every tool and piece of technology available is being used to look for the missing sub.

“Right now, our capability is limited to sonar buoys and listening for sound but we’re working very hard to increase the capability,” U.S. Coast Guard Rear Adm. John Mauger said.

Both the U.S. and Canadian Coast Guards have deployed American C-130 aircraft and a Canadian P8 Poseidon as part of the aerial search. A fleet of search and rescue boats remains searching in the water.

“And we are doing everything we can do to make sure we can locate and rescue those on board,” Mauger said.

Journalist David Pogue, who has traveled on the Titan, told NewsNation’s Elizabeth Vargas just how dangerous the ride is.

“You know, it’s not going to be Delta Airlines level safety. You sign a waiver. It says these are the different ways I could die. They outline it for you,” Pogue said.

OceanGate Expeditions, the U.S. company that owns and operates the Titan said in a statement, “Our entire focus is on the crew members in the submersible and their families. We are deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to reestablish contact with the submersible.”

“They’re first and foremost in our thoughts every moment of this search operation,” Mauger said.

The Titan is one of a kind. There’s no other vessel in the world that has its capabilities.

It’s also designed to float back to the surface on its own. Another reason why there’s so much concern is that there could be something preventing the sub from resurfacing even on its own.