Indonesia has deployed six warships within the look for a navy submarine that went missing with 53 people on board.
A helicopter and 400 people were also sent out on the hunt, the navy said.
Singapore and Malaysia have also dispatched rescue ships, while nations including the US, Australia, France, and Germany have offered help.
The KRI Nanggala-402 vessel had been conducting a drill north of the island of Bali on Wednesday but did not report back and contact was lost.
The German-made submarine is assumed to possess disappeared in waters about 60 miles (100km) off the coast of Bali early Wednesday morning.
“[The navy] is currently checking out it. we all know the world but it’s quite deep,” First Admiral Julius Widjojono told AFP press agency.
Some reports say contact was lost after the submarine had been given clearance to dive into deeper waters.
Meanwhile, an oil spill found near where a missing submarine dived could point to fuel tank damage, or could even be a sign from the crew, the Indonesian navy said.
The vessel is one among five submarines operated by Indonesia.
It was made within 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 among its submarines, a navy spokesman told the news channel.
But similar incidents have happened elsewhere. In 2017, an Argentine military submarine went missing within the southern Atlantic with 44 crew on board.
Its wreck was located a year later, and officials confirmed that the submarine had imploded.