Time is running out for the 53 crew members on a missing Indonesian submarine. Authorities say the vessel has less than 36 hours of oxygen left.

The Indonesian navy is racing against time to find and save the 53 crew members aboard the missing KRI Nanggala-402 submarine, as the vessel contains only enough oxygen to last until Saturday.

In a televised press conference on Thursday afternoon broadcast on the Indonesian news outlet Kompas TV, Indonesian officials said the submarine was equipped with only 72 hours of oxygen.

Over 36 hours has elapsed since the submarine disappeared in the waves off the coast of the Indonesian island of Bali at 3 a.m. local time on Wednesday. It was participating in a torpedo drill along the Bali Strait, a 37-mile stretch of water between the islands of Java and Bali that connects the Indian Ocean to the Bali Sea, when it went off the grid abruptly.

First Adm. Julius Widjojono, a representative for Indonesia’s Ministry of Defense, told members of the media on Wednesday that 49 crew members, one ship commander, and three weapons specialists were aboard the missing submarine.

“We cannot say for sure if the vessel has sunk, but if it has, the crew may be running out of oxygen,” Indonesian Defense Minister Prabowo Subianto said during the press conference, adding that a massive search-and-rescue operation was underway.

According to the BBC, the country has deployed six warships, a helicopter, and 400 military personnel in an attempt to locate and surface the vessel.

Channel News Asia reported that rescue vessels from Singapore and Malaysia were sent Thursday to help find the submarine.

Major Gen. Achmad Riad said at Thursday’s press conference that the navy was still searching for the submarine from the last position it was detected, which was about 23 nautical miles north of Bali. He added that he had no evidence to conclusively say the submarine had sunk.

The Indonesian navy lost contact with the submarine at about 4:30 a.m. local time. This means the search-and-rescue team has slightly over a day to find the vessel and surface it — or guide it to shallow waters, where rescuers can extract the crew.

According to Reuters, rescuers doing an aerial search spotted an oil spill near the submarine’s dive position at about 7 a.m. on Wednesday. Representatives from the Indonesian navy said the oil spill indicated the submarine’s fuel tank might have cracked because of water pressure or other factors, plunging it to 600 to 700 meters below sea level.

The 44-year-old German-made vessel, which has been in operation since the 1980s, was built to withstand water pressure at a maximum depth of about 250 meters.

The submarine expert Frank Owen, the secretary of the Submarine Institute of Australia, told Insider he could not speculate on whether the crew was still alive.

“If it has sunk in 700 meters of water, this is a problem because that is well below its maximum operating depth. I still retain hope that the submarine is in difficulty in terms of getting to the surface but is safe,” Owen said, adding that the incident would be survivable in this best-case scenario.

“The best way to get the crew out is for the submarine to get to the surface or to shallow water,” he said.