An Indonesian navy submarine has gone missing with 53 people on board, military officials say.
The KRI Nanggala-402 was conducting live-fire torpedo exercises north of the island of Bali when it lost contact at about 3:00am on Wednesday morning.
Some reports say contact was lost after the submarine had been given clearance to dive into deeper waters.
The submarine is thought to have fallen to a depth of between 600 and 700 metres.
The Indonesian Navy report also said that an oil slick was discovered at approximately 7:00am on Wednesday after a helicopter was sent to the last known position of the KRI Nanggala-402, although it has not been confirmed. But if confirmed it indicates that the fuel tank damage or cracking due to seawater pressure.
According to an internal Indonesian Navy report a distress signal was sent by the Indonesian authorities to the International Submarine Escape and Rescue Liaison Office (ISMERLO) on Wednesday afternoon.
ISMERLO coordinates international submarine search and rescue operations and the Singapore Navy and the Australian Navy responded to the distress signal, reports claimed.
Singapore dispatched a submarine rescue ship along with a Deep-Submergence Rescue Vessel (DSVR) to perform complex rescue operations. A medical team was also on board.
Indonesia and Singapore have signed a submarine rescue pact in 2012. Singapore has similar rescue agreements with Australia, South Korea, Vietnam, the United States and India.
The German-made submarine is one of five submarines operated by Indonesia.
It was made in the late 1970s, and underwent a two-year refit in South Korea that was completed in 2012. It is the first time Indonesia has lost one of its submarines, a Navy spokesman said.
Similar incidents have happened elsewhere. In 2017, an Argentine military submarine went missing in the southern Atlantic with 44 crew on board.
Its wreck was located a year later, and officials confirmed that the submarine had imploded.