Searches at the Titanic submersible site have picked up banging noises underwater, renewing hopes that rescue efforts may be successful.
US Coast Guard confirmed that search efforts have been relocated after "underwater noises" were detected in the area.
This comes as there's believed to be less than 30 hours of oxygen left on board the vessel.
Read More: Irish Titanic explorer confirms safety after tourist sub goes missing
Five people onboard the tourist vessel - named Titan - vanished when heading on an expedition to the Titanic wreck site on Sunday morning.
Communications were lost to the mothership MV Polar Prince around one hour and 45 minutes into the two-hour descent.
British billionaire Hamish Harding, British-based Pakistani businessman Shahzada Dawood, 48, and his son Sulaiman Dawood, 19; CEO of OceanGate Expeditions - the company which owns and operates the vessel - Stockton Rush and French submersible pilot Paul-Henry Nargeolet were all aboard the 22ft long single windowed sub.
The pilot's family live in Cork while Irishman Rory Golden is on the mothership MV Polar Prince as a member of the original expedition.
There appears to have been a breakthrough in the hunt for the sub after rescuers said they "detected underwater noises".
A Canadian aircraft detected the noises in the area near where the submersible was last known to be.
The shocking discovery was first shared via internal e-mails sent to the heads of the Department of Homeland Security, CNN reported.
This was followed by The Rolling Stone reporting that the "banging" was detected by a Canadian search aircraft, coming in 30 minute intervals on Wednesday.
The US outlet reported the email said: “RCC Halifax launched a P8, Poseidon, which has underwater detection capabilities from the air.
“The P8 deployed sonobuoys, which reported a contact in a position close to the distress position. The P8 heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed and banging was still heard.”
The US Coast Guard later confirmed the news, and confirmed they had relocated their search efforts as a result, but said despite the development there had been no results yet.
In a tweet, they said: "Canadian P-3 aircraft detected underwater noises in the search area. As a result, ROV operations were relocated in an attempt to explore the origin of the noises. Those ROV searches have yielded negative results but continue.
"Additionally, the data from the P-3 aircraft has been shared with our U.S. Navy experts for further analysis which will be considered in future search plans."
The Explorers Club, an international association that promotes scientific exploration and field study of which Mr Harding and Mr Nargeolet are members, said there were "signs of life".
Harding is a founding member of the board of trustees of The Explorers Club, which released a statement in which President Richard Garriot de Cayeux said: “There is cause for hope, that based on data from the field, we understand that likely signs of life have been detected at the site.
It continued: "Members of The Explorers Club far and wide rallied today to make sure the Titanic expedition search and rescue team is fully aware of the capabilities and experience club members and affiliates are ready to prove. This extraordinary membership never ceases to amaze.
"We continue to work on approval for the Magellan ROVs to be allowed to deploy to the site as we believe they can provide invaluable assistance.
"Our hearts are with family and friends of fellow Explorers Club members Hamish Harding and Paul-Henri Nargeolet, and the rest of the submersible crew as we await hopefully good news."
In an email sent on Tuesday afternoon, the president of the Explorers Club reportedly said the tapping might be the crew "signalling" to rescuers.
US Coast Guard have been leading a desperate search to try and locate the submarine amid concerns passengers only have enough oxygen to last until around midday Thursday.
At a press conference on the traumatising case that has captivated the world, held at 6pm BST on Tuesday, Coast Guard chiefs said the vessel had just 40 to 41 hours before their oxygen runs out, which would fall around the deadline.
It is understood the King is being kept informed of the search efforts, as Shahzada Dawood is a long-time supporter of The Prince’s Trust International and The British Asian Trust, both of which are charities founded by Charles.
So far, 10,000 square miles of sea has been searched during the race against time to locate the missing submersible.
The rescue effort has involved planes and ships in a unified command of US Coast Guard, US Navy, Canadian Coast Guard and OceanGate expedition.
The news comes after wreck hunter David Mearns, who is a friend of Harding, said he had seen reports of "tapping" being heard in the water.
He told Channel 4 News: "They’ve got sonobuoys out there; there may be some other hydrophones that the mothership, the Polar Prince, had in the water."
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