JAKARTA (AP): Indonesia's navy is searching for a submarine that went missing north of the resort island of Bali with 53 people on board, the military said Wednesday.

Military chief Hadi Tjahjanto said the KRI Nanggala 402 was participating in a training exercise when it missed a scheduled reporting call.

The submarine is believed to have disappeared in waters about 60 miles (95 kilometers) north of Bali, he said.

Tjahjanto said the navy has deployed scores of ships to search the area, including a hydrographic survey ship, and has asked for help from Singapore and Australia, which have submarine rescue vessels.

Local media reports said the navy believes the submarine sank into a trough at a depth of 700 meters (2,300 feet).

The Defence Ministry said in a statement that the submarine lost contact after being granted clearance to dive. It said a helicopter later spotted an oil spill near the dive's starting position.

It said the submarine was carrying 49 crew members, its commander and three gunners.

The German-built submarine, which has been in service in Indonesia since 1981, was rehearsing for a missile-firing exercise that was to take place on Thursday. Tjahjanto and other military leaders were to attend.

Indonesia currently has a fleet of five submarines and plans to operate at least eight by 2024.

The country, the world's largest archipelago nation with more than 17,000 islands, has faced growing challenges to its maritime claims in recent years, including numerous incidents involving Chinese vessels near the Natuna islands.

Last year, President Joko Widodo reaffirmed the country's sovereignty during a visit to the group of islands at the edge of the South China Sea.

His visit came a week after Chinese Foreign Ministry spokesperson Geng Shuang insisted that Chinese fishermen are free to conduct activities in the areas China claims as its traditional fishing grounds, which partly overlap Indonesia's exclusive economic zone.

Geng's statement drew indignation in Indonesia and prompted the military to increase its forces at the islands. Although China has been making such claims for years, recently dozens of Chinese fishing boats, escorted by coast guard vessels, reportedly made more aggressive moves in the area and ignored Indonesian warnings to leave.