Local tugboats and fishermen brought many of the survivors ashore after the KM Ladang Pertiwi sank while traveling through the Makassar Strait on Thursday.

"So far, 31 people have been rescued alive, and we are still looking for 11 more people who are still missing," the head of the local search and rescue team, Djunaidi, told AFP on Monday.

"They have returned home now, and they are generally in good health," he added.

Rescuers have deployed a helicopter and extended the search area to 20 nautical miles from where the boat sank in the search for the missing, Djunaidi said.

The vessel did not have a permit to transport passengers, he added, and both the ship's captain and owner had been taken in for questioning.

No official passenger manifest was kept – common in a country where crews sometimes sell illegal tickets past the ships' official capacity – but authorities have said they believe there were 42 people onboard when the boat sank.

Marine accidents are common in the country, where safety standards are often lax. 

In May, a ferry carrying more than 800 people ran aground in shallow waters off East Nusa Tenggara and remained stuck for two days before being dislodged. No one was hurt. 

In 2018 more than 150 people drowned when a ferry sank on Lake Toba in North Sumatra.

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