SIWA, Indonesia : Rescuers scoured a remote gulf Monday for survivors of a weekend ferry disaster in central Indonesia, as anguished relatives gathered desperate for news from a boat that has still not been found.

Nearly 80 people remain missing after a vessel carrying 118 passengers ran into trouble in rough seas Saturday as it crossed the southern gulf of Sulawesi island.

Three people have been confirmed dead and 39 rescued, but search teams have so far been unable to locate the stricken ferry, more than two days after it sent out a distress signal.

Six boats - including two fishing vessels - and one helicopter have been deployed to comb the gulf where the ferry vanished.

Distressed relatives have gathered in Siwa, the small port town to which the ferry was travelling, many clutching photos of the missing as they wait nervously for information.

50-year-old Sia said her niece telephoned Saturday afternoon from the ferry, saying the boat was having engine trouble and was taking on water.

"My niece and her husband have not been found," said Sia, who, like many Indonesians, goes by just one name. "I hope they will be found alive immediately."

Hasan, 67, said his nephew Wiwin, a technician on the boat, called him as the ferry struggled in a violent storm.

"He asked me to pray for him because the waves and currents were strong," Hasan said. "After that he said he had to go downstairs to check on the engine."

After two days of torrid weather, with huge waves and strong winds, rescue crews were granted a reprieve Monday, with calmer weather lifting spirits and hopes of finding survivors.

"The weather is quite good today, hopefully we will find more people," local rescue head Roki Asikin told AFP, adding his team was feeling optimistic as they set off at daybreak. "We are still searching for the survivors."

Some of those found alive were hauled from the water in life jackets after enduring a night in treacherous swells that surged up to five metres (16 feet).

Four others, including a young boy, were spotted by fishermen desperately clinging to fish traps and buoys, and were dragged aboard exhausted and taken to hospital.

In Sulawesi, a vast island in central Indonesia patterned with with large bays and gulfs, people are heavily dependent on ferry services to cut down travel time between distant provinces.

But across Indonesia - a sprawling archipelago of more than 17,000 islands - maritime accidents are common, with overcrowding, poor maintenance and treacherous weather often leading to disaster.

In June dozens of tourists were injured in several explosions on a ferry in eastern Indonesia, while more than 20 passengers died and a similar amount never found when a ferry sank in East Java last year.