(Adds local mayor, details)

JAKARTA, Oct 19 (Reuters) - An Indonesian ship that might have been overloaded with passengers capsized off the island of Sulawesi, killing around 30 people and leaving many missing, officials said on Friday.

The small wooden ship sank on Thursday night just before reaching the town of Baubau, in southeastern Sulawesi.

The mayor of Baubau said by telephone that 31 bodies had been recovered, including three babies, and 35 people had been reported missing. He said that 125 people had survived.

"We found the babies trapped between dead bodies too. People rushed to get out all together but then they were trapped instead," said Mayor Amirul Tamil.

"We had already urged people not to insist on getting onboard a few days ago. The boat was overloaded, but we could not do anything since the boat started sailing far away from Baubau."

Earlier, transport ministry spokesman Bambang Ervan said that 15 people had died, but Tamil and a Indonesian Red Cross official later said the figure was roughly double that.

"Preliminary investigations have indicated that the ship may have sunk because passengers piled onto one side ... tipping its balance and causing it to roll over," Ervan said.

Authorities were still investigating the cause but Ervan said the seas were calm at the time of the accident.

Mayor Tamil said the ship was towed back to shore and that some survivors were found clinging to the bottom of the vessel.

"Relatives of the dead have come to get the bodies and they get 500,000 rupiah ($55) of compensation," he said.

The mayor said that the manifest showed 188 passengers, excluding children and toddlers travelling with their parents.

It is often difficult to pin down the number of people on passenger ships in Indonesia, since official manifests are notoriously unreliable.

It is common for people to sneak on to ferries or bribe crew to let them aboard for less than the price of a ticket, meaning their names are not recorded.

Laode Hamdansyah, head of the Indonesian Red Cross in Baubau, said 29 bodies had been retrieved and that 200 might have been on board.

Hamdansyah said 40 Red Cross rescuers on three fishing boats, along with two marine police vessels, were scouring the seas for more survivors.

The safety record of Indonesian passenger ships and ferries, widely used to connect the thousands of islands in the archipelago, is poor with vessels frequently overloaded and in poor condition. ($1=9,085 Rupiah)

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