JAKARTA - The captain of a ferry which sank in Indonesian waters killing 29 people blamed a freak storm for the disaster Monday, despite suspicions the craft was overloaded.

As the search for survivors from the Dumai Express resumed off Karimun island, near Singapore, captain Johan Napitupulu said he had no warning he was sailing into a massive storm when he left Batam on Sunday.

"The weather was fine when we left Batam port. There was no sign of rain and we also didn't get any warning from anybody saying the weather could turn bad at sea," he told AFP.

"About half an hour later the weather suddenly turned really, really bad. The waves were higher than two metres (six feet), the winds and currents were strong."

He denied the vessel was overloaded or unfit to sail, and said the crew had done all it could to arrange life boats and jackets for the terrified passengers.

"The waves could have struck the front part of the ferry and caused it to crack, and water had got in.

"The ferry was sinking fast, front first. Within 27 minutes it was totally submerged.

"We told the passengers to put on life jackets and we launched four light craft, each with a capacity of 65 people. There was panic, everyone was screaming."

He said some fit male passengers were told to swim until help arrived. The official toll stood at 29 dead and 250 rescued as officials tried to piece together what caused the latest in a litany of ferry disasters in Indonesia.

Karimun-based Navy Lieutenant-Colonel Edwin said the boat's manifest listed only 242 passengers and crew including 15 children, indicating many of the passengers were unregistered.

"There's an indication of overcapacity," he told AFP.

"We resumed the search at 6:00 am (2300 GMT Sunday).... The chances of finding survivors are still high because they were wearing life jackets."

Heavy seas are preventing navy divers from finding the wreck to determine if anyone was trapped below decks, he said.

"At the moment the currents are very strong, it's raining and the waves are 2.5 metres high, so the risks are very high if we (try to search the wreck)," he said.

Napitupulu said: "From our checks, there wasn't anyone in the ferry when it sank."