Armed robbers boarded a chemical tanker off Malaysia on Saturday, stealing cash, laptops and mobile phones before escaping.
Malaysian authorities say the raid took place on a vessel called Bintang at Tanjung Piai near the Singapore border.
The eight men were carrying guns and machetes. They attacked crew in the engine room and tied them up, before escaping in a wooden boat.
Malaysian authorities said the same gang was probably responsible for a number of attacks in the area this month.
The Mongolian-flagged ship has a crew comprising 14 Burmese and two Sri Lankans.
Satellite data shows one Indonesian-controlled tanker named Bintang in the Singapore area, but the IMO number shows up as invalid in the Equasis database.