Rescue efforts have been hampered by choppy seas and high winds.

About 40 people have been accounted for, reports said yesterday, with many survivors sheltering on smaller vessels or nearby islands because of the bad weather.

The ship was travelling from the port of Kumai on the island of Borneo to Semarang on the main island of Java. A local police chief said the boat had only 200 listed passengers but most reports say the real number aboard the vessel was more than double that.

Ships and ferries are a cheap and popular means of transport between the 17,000 islands that make up Indonesia. Safety standards are not always enforced and vessels frequently carry more passengers then they are meant to.

The boat is thought to have sunk about 40 kilometres off Mandalika island, about 300km northeast of the capital, Jakarta. According to a naval official, the ship's crew contacted the coastguard shortly after midnight yesterday to say they had lost control of the vessel.

Rescue teams were ready at Semarang harbour since yesterday morning but massive waves and high winds prevented their boats from setting out. A survivor said passengers on the boat began praying as the waves rose around them. The man, who gave his name as Cholid, said passengers also fought over life jackets as the boat capsized.

"I was going upstairs to try to help my daughter, but the ship suddenly broke up and I was thrown out. I lost her, " he said.