JAKARTA, Indonesia (AP) — Indonesian navy ships were scouring the waters off Bali on Friday as they raced against time to find a submarine that disappeared two days ago and has less than a day’s supply of oxygen left for its 53 crew.

The KRI Nanggala 402 went missing after its last reported dive Wednesday off the resort island, and concern is mounting the submarine may have sunk too deep to reach or recover. The navy chief said the submarine was expected to run out of oxygen by around 3 a.m. Saturday.

“We will maximize the effort today, until the time limit tomorrow 3 a.m.,” military spokesperson Maj. Gen. Achmad Riad told reporters.

There have been no signs of life from the submarine, but the spokesperson refused to speculate on its fate.

A total of 24 navy and other ships and a patrol plane were being mobilized for Friday’s search with a focus on the area where an oil slick was found after the submarine disappeared during an exercise. Rescuers made similar massive searches in the past two days.

An Australian warship equipped with a sonar device and a helicopter was set to arrive later Friday. A second Australian warship as well as Singaporean and Malaysian rescue ships were also expected in the coming days.

“These two Australian ships will help expand the search area and extend the duration of search effort,” Australian Navy Rear Adm. Mark Hammond said.

Indonesian President Joko Widodo canceled a visit to Banyuwangi port, where some rescue ships left earlier, due to preparations for a weekend regional summit in Jakarta, officials said. He asked Indonesians to pray for the crew’s safe return, while ordering all-out efforts to locate the stricken submarine.

“Our main priority is the safety of 53 crew members,” Widodo said in a televised address on Thursday. “To the family of the crew members, I can understand your feelings and we are doing our best to save all crew members on board.”

There’s been no conclusive evidence the oil slick was from the sub. Navy Chief of Staff Adm. Yudo Margono said oil could have spilled from a crack in the submarine’s fuel tank or the crew could have released fuel and fluids to reduce the vessel’s weight so it could surface.

Margono said an unidentified object with high magnetism was located at a depth of 50 to 100 meters (165 to 330 feet) and officials held out hope it’s the submarine.

The navy also said it believes the submarine sank to a depth of 600-700 meters (2,000-2,300 feet), much deeper than its collapse depth at which water pressure would be greater than the hull could withstand. The vessel’s collapse depth was estimated at 200 meters (655 feet) by a South Korean company that refitted the vessel in 2009-2012.

The cause of the disappearance is still uncertain. The navy has said an electrical failure could have left the submarine unable to execute emergency procedures to resurface.

Pentagon press secretary John Kirby said the United States is sending airborne assets to assist in the search. “We are deeply saddened by the news of Indonesia’s lost submarine, and our thoughts are with the Indonesian sailors and their families,” Kirby said. Other countries have also offered assistance.

Submarine accidents are often disastrous.

In 2000, the Russian nuclear submarine Kursk suffered internal explosions and sank during maneuvers in the Barents Sea. Most of its 118 crew died instantly, but 23 men fled to a rear compartment before they later died, mainly of suffocation. In November 2017, an Argentine submarine went missing with 44 crew members in the South Atlantic, almost a year before its wreckage was found at a depth of 800 meters (2,625 feet).

But in 2005, seven men aboard a Russian mini-sub were rescued nearly three days after their vessel became snagged by fishing nets and cables in the Pacific Ocean. They had only six hours of oxygen left before reaching the surface.

The German-built diesel-powered KRI Nanggala 402 has been in service in Indonesia since 1981 and was carrying 49 crew members and three gunners as well as its commander, the Indonesian Defense Ministry said.

Indonesia, the world’s largest archipelago nation with more than 17,000 islands, has faced growing challenges to its maritime claims in recent years, including numerous incidents involving Chinese vessels near the Natuna islands.