Rescuers using sonar to search for the missing Titanic submersible with five people onboard detected underwater "banging" sounds in the North Atlantic where the craft vanished two days earlier, the US Coast Guard said on Twitter.
A Canadian aircraft detected underwater noises in the search area which led to the relocation of remotely operated vehicle's rescue operations "in an attempt to explore the origin of the noises," it said.
"Those ROV searches have yielded negative results but continue."
A Canadian aircraft involved in the search "heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed and banging was still heard," said an internal email sent to US Department of Homeland Security officials, according to Rolling Stone magazine.
A separate piece by CNN also reported the detection of banging sounds, citing an internal US Government memo that did not clarify when the noises were heard Tuesday, for how long or what might have caused them.
This comes amid growing fears for the five people aboard, as the vessel only had enough oxygen for up to 96 hours when it set out on Sunday morning.
On Tuesday, Jamie Frederick of the US Coast Guard said the submarine had "about 40 hours of breathable air" left.
Who was on board?
Prominent Pakistani businessman Shahzada Dawood and his son, Suleman, were on board the vessel in the North Atlantic, their family said in a statement. Dawood is the vice chairman of one of the largest conglomerates in Pakistan, Engro Corporation, which has stakes in fertilizers, vehicle manufacturing, energy and digital technologies.
British billionaire Hamish Harding is also among the passengers, according to a social media post from a family member. Harding had earlier posted about his expedition on Instagram that he was proud to join OceanGate's Titanic mission.
"Due to the worst winter in Newfoundland in 40 years, this mission is likely to be the first and only manned mission to the Titanic in 2023," he wrote.
OceanGate's founder and CEO Stockton Rush was also later confirmed by the company to be on board.
Rescuing passengers a 'phenomenally difficult challenge'
The rescue mission is a "phenomenally difficult challenge," said Simon Boxall, an academic in oceanography at the University of Southampton.
Speaking to DW on Tuesday, Boxall said part of the challenge is the long distance between the submersible and the nearest coast.
Boxall explained that rescue teams could either use a sound radar to sweep the seafloor in an effort to locate the submersible, or use cameras on unmanned vehicles. He said the latter was more feasible and therefore more likely.
"And, of course, once they've done that, they've still got the problem of how do they get it back to the surface. And, you know, this is fine if you've got months to do this. They've got two days to do this."
Boxall also addressed the challenges the rescue team might face with locating the submersible in a seabed saturated with the Titanic wreckage.
Speculating over what might have happened to the submersible, Boxall said it was likely immobilized and has lost its power. He speculated as a result that the vessel got caught on some of the wreckage in the seabed, or some of the fishing nets drifting about.
"No one knows. And until they can actually locate it and see it, then we've got no idea what the next stage will be."