KRI Nanggala 402 submarine that went missing off Bali with 53 people aboard earlier this week has "sunk," the Indonesian Navy said Saturday.

The Indonesian Navy's chief of staff Adm. Yudo Margono said a search party had recovered fragments from the KRI Nanggala 402 including items from inside the vessel, whose oxygen reserves were already believed to have run out.

Warships, planes and hundreds of military personnel have been searching for the stricken vessel. Authorities had said the German-built craft was equipped with enough oxygen for only three days after losing power.

That deadline passed early Saturday.

"We have raised the status from submiss to subsunk," Yudo told reporters, adding that the retrieved items could not have come from another vessel. "

(The items) would not have come outside the submarine if there was no external pressure or without damage to its torpedo launcher."

Navy officials displayed several items including a piece of its torpedo system and a bottle of grease used to lubricate a submarine's periscope.

They also found a prayer mat commonly used by Muslims. Indonesia is the world's most populous Islamic nation.

Margono said the hunt for the submarine — and sailors — would continue, but warned that deep waters made the recovery effort "very risky and difficult".

"We don't know about the victims' condition because we haven't found any of them. So we can't speculate," he said in response to questions about the possibility of survivors.

"But with the (discovery) of these items, you can make your own conclusion."

Search efforts for the KRI Nanggala-402 had been ongoing for several days while oxygen supply in the vessel was feared to have run out earlier Saturday.

The military said Saturday it has recovered debris from a submarine that went missing with 53 crew off the coast of Bali, including components and items from inside the stricken vessel.

Earlier, searchers have recovered debris believed to be from the missing submarine.

Yudo earlier said a scan had detected the submarine at 850 metres (2,788 feet), well beyond its survivable limits. The submarine, which disappeared as it prepared to conduct a torpedo drill, is designed to withstand a depth of up to 500 metres (1,640 ft).