Debris has been found near the Titanic during search for submersible, US Coast Guard says

The Coast Guard's post on Twitter did not say whether officials believe the debris is connected to the Titan, which was on an expedition to view the wreckage of the Titanic. It said the debris was discovered within the search area by a remotely operated underwater robot, and was being evaluated.

The Titan was estimated to have about a four-day supply of breathable air when it launched Sunday morning in the North Atlantic—but experts have emphasized that was an imprecise approximation to begin with and could be extended if passengers have taken measures to conserve breathable air. And it's not known if they survived since the sub's disappearance.

Rescuers have rushed ships, planes and other equipment to the site of the disappearance. On Thursday, the U.S. Coast Guard said an undersea robot sent by a Canadian ship had reached the , while a French research institute said a deep-diving robot with cameras, lights and arms also joined the operation.

Authorities are hoping underwater sounds might help narrow their search, whose coverage area has been expanded to thousands of miles—twice the size of Connecticut and in waters 2 1/2 miles (4 kilometers) deep. Coast Guard officials said underwater noises were detected in the search area Tuesday and Wednesday.

This undated image provided by OceanGate Expeditions in June 2021 shows the company's Titan submersible. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night. Credit: OceanGate Expeditions via AP, File

This photo provided by OceanGate Expeditions shows a submersible vessel named Titan used to visit the wreckage site of the Titanic. In a race against the clock on the high seas, an expanding international armada of ships and airplanes searched Tuesday, June 20, 2023, for the submersible that vanished in the North Atlantic while taking five people down to the wreck of the Titanic. Credit: OceanGate Expeditions via AP

OceanGate CEO Stockton Rush emerges from the hatch atop the OceanGate submarine Cyclops 1 in the San Juan Islands, Wash., on Sept. 12, 2018. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night, June 18, 2023. Credit: Alan Berner/The Seattle Times via AP, File

This photo combo shows from left, Shahzada Dawood, Suleman Dawood, Paul-Henry Nargeolet, Stockton Rush, and Hamish Harding are facing critical danger aboard a small submersible that went missing in the Atlantic Ocean. The race is on to find the Titan, which has an oxygen supply that is expected to run out early Thursday, June 22, 2023. Credit: AP Photo/File

The logo for an OceanGate Expeditions 2019 Titanic expedition is seen on a marine industrial warehouse office door in Everett, Wash., Tuesday, June 20, 2023. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night. Credit: AP Photo/Ed Komenda, File

Submersible pilot Randy Holt, right, communicates with the support boat as he and Stockton Rush, left, CEO and Co-Founder of OceanGate, dive in the company's submersible, "Antipodes," about three miles off the coast of Fort Lauderdale, Fla., June 28, 2013. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night, June 18, 2023. Credit: AP Photo/Wilfredo Lee, File

In this image released by Action Aviation, the submersible Titan is prepared for a dive into a remote area of the Atlantic Ocean on an expedition to the Titanic on Sunday, June 18, 2023. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night. Credit: Action Aviation via AP, File

U.S. Coast Guard Capt. Jamie Frederick, right, faces reporters as Royal Navy Lt Cdr Rich Kantharia, left, looks on during a news conference, Wednesday, June 21, 2023, at Coast Guard Base Boston, in Boston. The U.S. Coast Guard says sounds and banging noises have been heard from the search area for Titanic submersible. Credit: AP Photo/Steven Senne

The U.S. Coast Guard Cutter Warren Deyampert is docked as a member of the Coast Guard walks past, Tuesday, June 20, 2023, at Coast Guard Base Boston, in Boston. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night, June 18, 2023. Credit: AP Photo/Steven Senne, File

This 2004 photo provided by the Institute for Exploration, Center for Archaeological Oceanography/University of Rhode Island/NOAA Office of Ocean Exploration, shows the remains of a coat and boots in the mud on the sea bed near the Titanic's stern. Rescuers are racing against time to find the missing submersible carrying five people, who were reported overdue Sunday night, June 18, 2023. Credit: Institute for Exploration, Center for Archaeological Oceanography/University of Rhode Island/NOAA Office of Ocean Exploration, File

U.S. Coast Guard Capt. Jamie Frederick, left, faces reporters as Carl Hartsfield, director and senior program manager Oceanographic Systems Laboratory, center, and Paul Hankins, U.S. Navy civilian contractor, supervisor of salvage, right, look on during a news conference, Wednesday, June 21, 2023, at Coast Guard Base Boston, in Boston. The U.S. Coast Guard says sounds and banging noises have been heard from the search area for Titanic submersible. Credit: AP Photo/Steven Senne

U.S. Coast Guard Capt. Jamie Frederick, center at microphone, faces reporters during a news conference, Wednesday, June 21, 2023, at Coast Guard Base Boston, in Boston. The U.S. Coast Guard says sounds and banging noises have been heard from the search area for Titanic submersible. Credit: AP Photo/Steven Senne