The boat sank shortly after midnight about 2 nautical miles (3.7 kilometers) from shore on the outskirts of Kuala Lumpur while trying to leave Malaysia illegally, said the agency's official, who declined to be named because he was not authorized to speak to the media.

He said that the Indonesians, including women and children, were believed to be heading home ahead of the start of the holy Muslim month of Ramadan.

Thirty-one people have been rescued so far, the official said. A ship and several boats were searching for survivors and a helicopter will soon be dispatched, he said.

No reason was immediately given for the accident.

Tens of thousands of Indonesians work illegally in plantations and other industries in Malaysia. They sometimes risk dangerous boat journeys to return home.