A submarine with 53 crew members on board has disappeared off the coast of Bali

• The submarine was participating in a naval exercise near Bali when it went off the grid.
• The Indonesian navy is searching for the submarine, which was carrying 53 crew members.
• Search-and-rescue teams found an oil spill near the waters where the submarine was last spotted.

The Indonesian navy is searching for a submarine that went missing off the coast of Bali during a training exercise with 53 crew members on board.

Indonesia's Ministry of Defense spokesperson, First Admiral Julius Widjojono, said during a press conference on Wednesday that 49 crew members, one ship commander, and three weapons specialists were on board the submarine, which abruptly disappeared off the grid in the early hours on Wednesday.

The 44-year-old German-made submarine was participating in a torpedo drill being carried out in the Bali Strait, a 37-mile long stretch of water between the islands of Java and Bali, that connects the Indian Ocean to the Bali Sea.

The KRI Nanggala-402 lost contact during a dive at around 4.30 a.m. local time on Wednesday. This was close to one and a half hours after the submarine asked for "permission to dive" from the exercise's task force at around 3 a.m.

According to Reuters, an aerial search revealed an oil spill near the dive position at around 7 a.m. local time on Wednesday.

The Indonesian Navy said in a statement on Wednesday that a "blackout" may have occurred in the submarine.

"It is possible that during static diving, a blackout occurred so control was lost and emergency procedures cannot be carried out and the ship fell to a depth of 600 to 700 meters," the statement said.

In a televised interview aired on local news station TVRI, representatives from the Indonesian navy said that the oil spill indicated that the submarine's fuel tank might have cracked due to water pressure or other factors.

Indonesian officials added that this particular model of the submarine was built to withstand pressure at a maximum depth of around 250 meters.

Submarine expert Frank Owen, secretary at the Submarine Institute of Australia, told Insider that he could not speculate on whether or not the crew of the submarine 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.

Al Jazeera reported that Indonesia used to operate a fleet of 12 submarines bought from the Soviet Union, but it now only owns a fleet of five.

These include two German-built vessels and three newer South Korean submarines.

However, the German-built submarines - which include the missing vessel - have been in operation since the 1980s. The KRI Nanggala-402 most recently went through a refit in 2012.

The Indonesian Defense Ministry told Reuters Thursday morning that search operations were still being conducted some 60 miles from the coast of Bali. At the time of this article's publishing, the vessel is still missing

Channel News Asia reported on Thursday that rescue vessels from Singapore and Malaysia will be deployed to help find the submarine.