Indonesian rescuers have found five more survivors, including a seven-year-old girl, from a passenger boat that sank off the country's eastern coast earlier this week, while search operations continue for 20 people who remain missing.

The KM Nurul Salsa, carrying 78 passengers and crew, suffered engine failure before sinking on Wednesday about 43 nautical miles (79 kilometres) from a port in the Selayar Islands of South Sulawesi province.

Makassar Search and Rescue Office chief Muhammad Arif Anwar said the five survivors — one man and four women — were discovered late Saturday clinging to a floating fish trap owned by a local fisherman. They were spotted before nightfall and rescued by a passing fishing boat near Matallang Island before being transferred to a search and rescue vessel.

The survivors were later taken to Benteng port for medical examinations and to provide information to investigators, Anwar said.

Authorities have confirmed one death from the incident so far, while efforts are continuing to locate the remaining missing passengers.

Officials also revised the number of people on board, saying the vessel had been carrying 78 passengers and crew, up from an earlier estimate of 74.

Passenger boats remain a vital means of transport across Indonesia, an archipelago of more than 17,000 islands. However, marine accidents are relatively common due to overcrowding, poor safety standards and inadequate enforcement of maritime regulations.