There have been claims that the ferry was overcrowded
An Indonesian ferry that sank at the weekend may have been carrying 103 more people than the 267 listed on its ship's manifest, officials say.
However, they say it is too early to conclude that they were all additional passengers and some may have travelled under different names.
The Teratai Prima ferry sank just before dawn on Sunday off Sulawesi island in heavy seas.
Only 35 survivors have been found since the vessel went down.
Recent years have seen several ferry accidents in Indonesia. More than 400 people died when a ferry sank in 2006.
"Based on reports from relatives there were at least 103 passengers who were not listed on the boat's manifest," Indonesian Transport Ministry spokesman Bambang Erfan said.
But he stressed that the numbers could be misleading.
"We're investigating whether they [passengers] used different names like nicknames or there were more passengers than the number registered."
The Teratai Prima ferry was making an overnight journey from Pare Pare in South Sulawesi to Samarinda in East Kalimantan when it sank.
Survivors said high waves flipped the ferry over. Most passengers were asleep and had little time to react.
"I felt that the ferry was listing to the left, then suddenly it turned upside down," said 29-year-old Yulianus Mangande, who was picked up by fishermen.
"I had to swim in the dark in heavy seas until the morning."
One survivor said he had scrambled into a life raft after clinging to a piece of wood.
"I grabbed my son on my back and swam to a piece of wood, but my son disappeared after being hit by a big wave," said Daeng Gassing, whose father-in-law was also missing.
RECENT MARITIME DISASTERS
11 July 2007: Passenger ship with 70 on board sinks off eastern Indonesia
22 Feb 2007: At least 42 die as ferry catches fire
30 Dec 2006: More than 400 lost as ferry sinks between Borneo and Java
7 July 2005: About 200 die as ferry sinks off eastern Indonesia
Officials are also examining why the ship's captain, who survived, set sail despite storm warnings.
Indonesia relies heavily on ferry services to connect the main islands in the archipelago, but accidents are common.
In December 2006, a ferry carrying more than 600 people sank while on a journey from Borneo to Java. The majority of its passengers were never found.
Months later, at least 42 people were killed when a fire broke out aboard a ferry from Jakarta to Bangka island off Sumatra.