The Indonesian air safety agency has called for better pilot fatigue monitoring mechanisms, after an investigation revealed that both pilots of a commercial aircraft had recently fallen asleep in-flight.

A pilot and co-pilot were simultaneously asleep for approximately 28 minutes during a Batik Air flight from South East Sulawesi to the capital Jakarta on January 25, a preliminary report by the National Transportation Safety Committee (KNKT) said.

The report, seen by AFP on Friday, was uploaded to the agency's website in late February.

Indonesia is a vast archipelago with a poor air safety record, despite relying heavily on air transport to connect its thousands of islands.

One of the pilots had not rested adequately on the night before the flight, the report said.

The incident resulted in a series of navigation errors, but the Airbus A320's 153 passengers and four flight attendants were unharmed during the two-hour-and-35-minute flight.

About half an hour after the plane took off, the captain asked permission from his second-in-command to rest for a while, with the request being granted.

The co-pilot then took over command of the aircraft, but also inadvertently fell asleep, the report said.

"The second-in-command had one-month twin babies. His wife took care of the babies and he assisted while at home," the report said.

A few minutes after the last recorded transmission by the co-pilot, the area control centre in Jakarta tried to contact the aircraft. It received no answer.

Twenty-eight minutes after the last recorded transmission, the pilot woke up and realised his co-pilot was asleep and that the aircraft was not on the correct flight path.

He immediately woke his colleague up, responded to the calls from Jakarta and corrected the flight path, the report said.

The plane landed safely after the incident.

Investigators did not identify the pilots, but said they were both Indonesians and were aged 32 and 28.

KNKT urged Batik Air to create detailed procedures to conduct proper and regular cockpit checks and to ensure that pilots and cabin crew were well-rested before their flights.

Batik Air did not immediately respond to questions when contacted by AFP.