A mysterious object with a "high magnetic force" has been detected floating in seas near where a submarine vanished with 53 people on board.
Yudo Margono, the navy chief of staff, told reporters authorities had found an item with "high magnetic force" floating at a depth of 50 to 100 metres.
Authorities are hopeful the object may be the missing submarine and are now awaiting a navy ship that has underwater detection facilities that will help them investigate the object further.
Indonesia's military has so far refused to comment about whether the decades-old submarine, carrying 53 crew, was over capacity.
But it has said the submarine might have sunk to vast depths after a blackout that left its crew powerless to control the vessel.
The ABC reports if the detected object is part of the submarine, the navy suspects the crew could have released its fuel load after a possible loss of power to allow the submarine to float.
Navy officials fear the submarine could have sunk to deaths where it most likely would implode.
Collin Koh, a naval affairs specialist and research fellow at the S. Rajaratnam School of International Studies in Singapore, also said damage to the fuel tank could "spell big trouble".
"If your tank's cracked it is not very good news," he said.
"Because we are talking about the pressure hull of the submarine being breached. So it could cause potential flooding."
There are grave fears for the submarine, with navy spokesman Julius Widjojono earlier telling KompasTV that the diesel-powered submarine that runs on electric batteries while submerged could only sustain a depth of 250 to 500 metres.
"Anything more than that can be pretty fatal, dangerous," he said.
The seas in the area are shallower than in other parts of the archipelago but can still reach depths of more than 1,500 metres.
Grave fears over lack of oxygen on submarine
The crew on the KRI Nanggala 402 could have enough oxygen until early Saturday, but time is running out as rescuers scour the coast off holiday island Bali where it disappeared.
"There's time until Saturday around 3am. Let's hope we can find them before then," Margono told reporters.
However, defence analysts have warned that the vessel could have already broken into pieces if it has sunk to depths believed to be as much as 700 metres — well below what it was built to withstand.
Indonesia's president Joko Widodo asked his country to pray for the crew, while Australian Defence Minister Peter Dutton said initial reports raised the prospect of a "terrible tragedy".
He told 2GB radio that the fact that the submarine is “in a very deep part of waters” makes it “very difficult for the recovery or for location".
'Race against time'
The exact location of the vessel has yet to be pinpointed, the navy said, with warships and helicopters assisting in the hunt.
Neighbouring Singapore and Malaysia have already dispatched ships that are expected to arrive in the coming days, including the city-state's MV Swift Rescue — a submarine rescue vessel.
India said Thursday it had sent a ship to assist in the hunt, while the United States, Australia, France and Germany are among other nations that have offered help.
As the Royal Australian Navy’s senior serving submariner and Commander of the Australian Fleet, my thoughts are with the Indonesian Navy, their submariners and their families and friends at this difficult time. 🇦🇺🇮🇩 pic.twitter.com/q0D4GMfr4G
— Commander Australian Fleet (@COMAUSFLT) April 22, 2021
"There are too many unknowns right now," said Curie Maharani, a defence expert at Indonesia's Bina Nusantara university.
"But what we do know is that it's a race against time."
Frank Owen, secretary of the Submarine Institute of Australia, warned that rescuing any surviving crew quickly would be near impossible.
"If the submarine is on the seabed, and if it is in the depth of water that is there, there is little they can do to actually get the people out," he said.
with AFP and AAP
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