The U.S. Coast Guard announced via Twitter late Thursday morning that "a debris field was discovered within the search area by" a remotely operated vehicle (ROV) "near the Titanic" wreckage.

"Experts within the unified command are evaluating the information," the U.S. Coast Guard tweeted.

The Coast Guard is set to hold a briefing on the findings from the Horizon Arctic's ROV at 3 p.m. ET.

Despite their onboard oxygen tank expected to be depleted sometime Thursday morning, one doctor says they may have more time if the passengers are still alive. He estimates the five people aboard the lost Titanic tourist sub could survive for 10 to 20 hours with air still circulating through the experimental capsule.

Dr. Richard Moon, a professor of anesthesiology at Duke University, said that despite conditions being dire, those aboard the OceanGate Expedition's submersible could extend the oxygen available after its tank is depleted by staying calm and moving as little as possible.

"The actual amount of time that they have is unpredictable, but it's probably less than 24 hours after the final oxygen in the tank is depleted," Moon, director of the Duke Center for Hyperbaric Medicine and Environmental Physiology, told ABC News.

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-ABC News' Bill Hutchinson

The U.S. Coast Guard announced via Twitter on Thursday morning that a remotely operated vehicle (ROV) deployed by the French vessel L'Atalante has entered the water in the search area.

The U.S. Coast Guard also gave an update on the conditions at sea, saying winds were at 14 mph with gusts up to 19 mph, swells were 4 to 5 feet and the air temperature was 50 degrees Fahrenheit.

The U.S. Coast Guard announced via Twitter early Thursday that a remotely operated vehicle (ROV) deployed by the Canadian vessel Horizon Arctic has reached the sea floor, beginning its search for the missing submersible.

Meanwhile, the French vessel L'Atalante is preparing its ROV to enter the water in the search area, the U.S. Coast Guard said.

Rescuers racing against the clock to save the five people trapped in a tourist submersible nearly two miles deep in the Atlantic Ocean are facing major obstacles that could make saving the people onboard extremely difficult, according to a former U.S. Navy submarine commander.

Retired Capt. David Marquet told ABC News on Monday that this type of rescue operation is complicated because there aren’t nearby U.S. or Canadian underwater vessels that can go as deep as the Titanic wreckage, which sits 13,400 feet below the ocean’s surface. Also, the ocean is pitch black at that depth.

"The odds are against them," Marquet said. "There's a ship in Boston that has this ability to either lower cable and connect to it or have a claw. It's still a thousand miles away."

Even if a vessel was able to locate the submersible and lower a cable, it’s extremely difficult to safely navigate the waters and attach it, according to Marquet.

"You've got to get it exactly right," he told ABC News. "It's sort of like ... getting one of those toys out of those arcade machines. In general, you miss."

Rescuers do have one advantage, Marquet said, as weather conditions off the coast of Newfoundland are not rough and will not disturb any boat or vessel there.

Marquet added that if the five people aboard are still alive, they would be asked to sleep to conserve their oxygen.

"We would put the vast majority of the crew to sleep because that's when you're using the least amount of oxygen and you're expelling the least amount of carbon dioxide," he said.

-ABC News' Sam Sweeney and Ivan Pereira