Relatives of some 230 people listed as missing three days after a ferry sank without trace in Indonesia's Makassar Strait angrily demanded the government step up search efforts Wednesday.

Only 35 survivors and two bodies have been found in the treacherous strait off western Sulawesi since the ferry went down early Sunday, and authorities admit there is little chance more of the missing people will be found alive.

But relatives waiting anxiously for news at search coordination centres on Sulawesi island refused to give up hope and complained that the government was not doing enough to find their loved ones.

About 50 people protested at the crisis centre in Majene, one of the closest towns to the spot where the 700-tonne Teratai Prima capsized and sank with 267 people on board after being hit by a tropical storm.

"The rescuers are just sitting around wasting time and money," said Abet, who had 63 relatives and neighbours from one village listed as missing.

"They blamed bad weather for stopping the search yesterday but how come fishermen still managed to find survivors? Why didn't the rescue teams find any?"

Some of the protesters pooled funds to hire three fishing boats to launch their own search.

"Why doesn't the government just give fishermen money to rent boats and do the search themselves? It would be more effective," Abet said.

Zeth Parante, whose wife and 10-month-old baby are missing, said: "I'm becoming very worried and fearful that my loved ones won't be found alive. This is the fourth day. They must be very hungry, exhausted and cold out at sea."

The navy and air force have been helping local rescue teams look for survivors since Sunday but their operations have been hampered by heavy rain and high seas.

Many of the survivors rescued so far have been found by fishermen and passing cargo ships.

Transport ministry official Sunaryo said more warships and helicopters had been deployed on Wednesday, but with so few bodies found, it appeared most of the missing passengers and crew were trapped in the sunken ship.

"My theory is that the ferry's passengers are trapped inside the wreckage under the sea," he said.

"The ferry sank in the middle of the night while passengers were asleep, and it sank very fast making it impossible for them to flee."

He said a navy warship was searching for the wreck of the ferry on the seabed at a depth of about 1,800 metres (6,000 feet).

Investigators were working to find out what happened amid allegations that the captain had ignored storm warnings and authorities had allowed the ferry to exceed its load capacity.

Sunaryo said investigators, including experts from Australia who would assist under a previous cooperation agreement, would look at why the captain, who survived, ignored the storm warnings when he sailed on Saturday afternoon.

It was the worst disaster of its kind in Indonesia since December 2006 when a ferry sank in a storm off the coast of Java, killing more than 500 people, although smaller ferries sink regularly across the massive archipelago.

President Susilo Bambang Yudhoyono vowed to improve safety standards after the 2006 disaster but Indonesians continue to die almost every month in ferry accidents.

The president, facing an re-election battle mid-next year, has made no public comment about the latest disaster.

"We need to do some reforms in all fields related to sea transport so that it meets international standards," maritime transport department official Abdul Gani said.