BALI (AFP) - Indonesia said on Friday (April 30) that it will salvage a submarine that sank off the coast of Bali, as grieving relatives paid their respects to the dozens of sailors killed in the disaster.

The authorities had yet to confirm if they would try to haul up the KRI Nanggala 402 from the sea floor, after it was spotted cracked in three pieces.

The navy on Friday said it was waiting on the arrival of two ships, including a vessel sent by China, that are equipped to handle deep-sea salvage operations.

High-powered magnets and air balloons were among the possible options, but how and when the cracked submarine would be brought to the surface was uncertain, said navy chief Yudo Margono.

"It's hard to talk about specific timing, but I can say that as soon as help arrives, we'll start," he told reporters.

The submarine's 53-strong crew is believed to still be inside the vessel, Admiral Margono said.

An underwater rescue vehicle supplied by neighbouring Singapore gave visual confirmation that the German-built boat was lying on the sea floor more than 800m deep.

The eerie images were final confirmation that there was no hope of finding survivors.

On Friday, victims' families cast flowers from a navy ship into waters where the submarine went down as part of a remembrance ceremony.

The submarine - one of five in Indonesia's fleet - disappeared on April 21 while it was scheduled to take part in live torpedo training exercises.

The crew asked for permission to dive. It lost contact shortly after.

Later, search teams spotted an oil spill where the vessel was thought to have submerged, pointing to possible fuel tank damage and a catastrophic accident.

The military has yet to offer an official explanation for the sinking of the decades-old submarine, which was delivered to the South-east Asian nation in 1981.

It has said, however, that the reconditioned vessel was seaworthy and discounted the possibility of an explosion.

The navy has said that the submarine may have suffered a blackout, leaving the crew unable to perform emergency measures.

Its hull would have been torn apart as it sank to depths far below what the KRI Nanggala was built to withstand, the navy added.

The submarine's former commander, Rear Admiral Muhammad Ali, has told local media that a so-called internal solitary wave could have been to blame.

The natural phenomenon occurs when different sea depths come together, creating forces that could have dragged the vessel down, he said.