There could be a glimmer of hope in the search for a missing submersible, with a deep-sea robot that can reach the depths of the Titanic expected to arrive at the search site very shortly.
Time is running out for the group on board, with under 12 hours of oxygen left as rescuers scramble to find the missing Titan submersible.
An extensive rescue mission was sparked after the submersible vessel on a tourist expedition lost contact an hour and 45 minutes into a 12,500 feet descent towards the Titanic wreck in the North Atlantic Ocean.
The vessel launched on Sunday morning (local time) carrying five men aboard, the founder and CEO of the vessel's US-based operating company OceanGate, a British billionaire, a Pakistani businessman and his 19-year-old son, and a French explorer.
Search and rescue teams have access to cutting-edge gear that is being used to help find the missing Titan.
One piece of equipment that is being rushed to the search site aboard the French research vessel L'Atalante and expected to arrive on Thursday afternoon (NZ time) is a deep-sea robot called Victor 6000.
Victor is a three-metre-long, remote-controlled robot with a bright yellow back and has been described as a "flagship device for underwater operations", by the French network BMTV, and is capable of reaching a depth of 6000 metres.
It has arms that can be remotely controlled to cut cables or otherwise help release a stuck vessel. But it doesn't have the capability of lifting the submersible on its own.
With the Titanic lying 3800 metres beneath the waves on the ocean floor, Victor should be more than capable of reaching it.
Newshub US Correspondent Mitch McCann told Newhsub at 11:30 that Victor could be a key tool in the frantic search for Titan.
"[It] can submerge to the ultra-deep depths of the Titanic, which is around 3800 metres below the surface," McCann said.
"So it could help untangle or site the submersible if it is in the correct area... the only problem with Victor is it moves very, very slowly. So they need to find the submersibles sooner rather than later."
But with oxygen running out in the Titan, hope is starting to dwindle for a successful rescue of the five men on board the submarine.
"Well, quite frankly, it's hard to be optimistic, isn't it? That vessel is running out of oxygen and those noises that were heard by the Canadian aircraft or detected under the water really haven't come to mind," McCann said.
It comes after the US Coast Guard said banging sounds had been detected in the ocean over the last couple of days sparking hope the missing group is still alive.
The underwater sounds were detected by sonar devices deployed to find the vessel, prompting a relocation of resources to explore its origin, which still remains unknown.
US Coast Guard Cpt James Frederick told media on Thursday morning (NZ time) he didn't know what the noises are but said they were searching the area of the noises and remained "optimistic and hopeful".
"We need to have hope but I can't tell you what the noises are. But what I can tell you is and I think this is the most important point, we're searching where the noises are and that's all we can do at this point."
Carl Hartsfield, of the Woods Hole Oceanographic Institution, told media at the press conference the noises have been described as banging sounds, but also said it was difficult to discern the source of noises underwater.
"They have to put the whole picture together in context and they have to eliminate potential manmade sources other than the Titan," Hartsfield said.
But a former Australian submarine officer and now search-and-rescue director is confident the noises are coming from inside of the Titan, as those aboard are well trained in emergency submarine situations.
"This tells me a huge amount," he said.
"Onboard the Titan is the French former Navy diver, the Titanic expert [Paul-Henri Nargeolet]. But also because he's a diver, he understands the way search forces look for submarines that are lost ... submariners are taught that if they're stuck in a disabled submarine on the hour and the half-hour they bang the hull for three minutes, then they stop. They don't make any more noise."
He added, "So the fact we're hearing banging at 30-minute internals tells me that the people inside are sending a message that says, 'We understand that you would be looking for us and this is how you might expect us to react.' So, it's very encouraging."
But even with time running out, the US Coast Guard is holding out hope for a successful rescue of the Titan and the men on board.
Frederick stressed the operation is still a "search and rescue mission, 100 percent".
