ALI, April 24 (AFP) - Hopes of rescuing dozens aboard a missing Indonesian submarine faded Saturday (Apr 24) as its oxygen reserves were believed to have run out, turning the focus to retrieving the stricken vessel from waters off Bali.

As hundreds of military personnel took part in a frantic hunt for the KRI Nanggala 402, authorities said the German-built craft was equipped with enough oxygen for only three days after losing power.

But that deadline passed early Saturday with still no sign of the missing vessel and its 53 crew.

The submarine - one of five in Indonesia's fleet - disappeared early Wednesday during live torpedo training exercises off the Indonesian holiday island.

Despite hopes for a miracle, an oil spill spotted where the submarine is thought to have submerged pointed to possible fuel-tank damage, fanning fears of a deadly disaster.

There were concerns that the submarine could have broken apart as it sunk to depths reaching 700m - well below what it was built to withstand.

The vessel was scheduled to conduct the training exercises when it asked for permission to dive. It lost contact shortly after.

Authorities have not offered possible explanations for the submarine's sudden disappearance or commented on questions about whether the decades-old vessel was overloaded.

Neighbouring Singapore and Malaysia as well as the United States and Australia were among nations helping in the hunt with nearly two dozen warships deployed to scour a search zone covering about 34 sq km.

On Thursday, Indonesia's military said it had picked up signs of an object with high magnetism at a depth of between 50 and 100 metre, bolstering hopes of finding the submarine.

But the passing of Saturday's oxygen deadline was likely to add the Southeast Asian archipelago to a list of countries struck by fatal submarine accidents.

Among the worst was the 2000 sinking of the Kursk, the pride of Russia's Northern Fleet.

That submarine was on manoeuvres in the Barents Sea when it sank with the loss of all 118 aboard. An inquiry found a torpedo had exploded, detonating all the others.

Most of its crew died instantly but some survived for several days before suffocating.

In 2003, 70 Chinese naval officers and crew were killed, apparently suffocated, in an accident on a Ming-class submarine during exercises in 2003.

Five years later, 20 people were killed by poisonous gas when a fire extinguishing system was accidentally activated on a Russian submarine being tested in the Sea of Japan.

And in 2018, authorities found the wreckage of an Argentine submarine that had gone missing a year earlier with 44 sailors aboard.