Indonesian submarine KRI Nanggala 402 is believed to have run out of its oxygen. Authorities said the German-built vessel had a built-in oxygen capacity of three days after losing power.
However, the three-day deadline came early Saturday with no sign of the craft dimming chances of survival for the 53 person crew aboard the submarine.
It lost contact shortly on Wednesday after it asked for permission to dive into the water during the scheduled training exercise.
Hundreds of military personnel took part in a frantic hunt to find the submarine that went missing amidst a live torpedo training exercise off the Indonesian holiday island, reported AFP.
Malaysia, Singapore, Australia and the United States all offered help and joined the hunt with about two dozens warships to scan and search a search zone covering about 10 square nautical miles (34 square kilometres).
An oil spill spotted over the spot where the submarine is believed to have submerged indicates possible damage to the tank and heightens fears of a deadly disaster. There have been speculations that the vessel may have broken apart as it sunk deep into the water believed to reach as deep as 700 metres (2,300 feet), much below what the german built submarine s built to sustain.
Indonesia's military on Thursday reported that it detected signs of an object with high magnetism at a depth of between 50 and 100 metres (165 and 330 feet), reinforcing hopes of finding the craft.
Authorities are yet to give any plausible explanations for the submarine's sudden disappearance or give a statement on questions about the vessel possibly being overloaded, reported AFP.