At least 18 people are dead and dozens missing after a boat carrying nearly 100 suspected migrant workers capsized and sunk in Indonesian waters, police said Wednesday.

The speedboat was ferrying 93 passengers from Malaysia to Batam, an Indonesian island just south of Singapore, when it sank, local police chief Sam Budi Gusdian said.

"Eighteen people have been found dead," he told reporters, adding 39 passengers had been pulled alive from the seas.

The fate of the 36 other missing passengers remains unclear. Search and rescue teams were combing the seas for any sign of survivors, Gusdian said.

The Indonesian archipelago of more than 17,000 islands is heavily dependent on boat transport, but fatal accidents are common.

More than 60 people died in December when huge waves capsized a ferry charting a course through Sulawesi province.