The 4,999-dwt Naniwa Maru No 1 (built 1992) was boarded by six armed pirates at around 1am local, Malaysian maritime police said on Wednesday.
Reports say the pirates also offloaded over 5m litres of diesel from the hijacked ship into two waiting vessels.
The Japanese-flagged tanker, which was en route to Myanmar from Singapore, had Indonesian, Thai, Myanmar and Indian crew members.
In October and November last year two similar incidents took place off the coast of Malaysia that also involved the theft of cargo.
Unnamed regional security officials, quoted by Reuters, said that armed gangs prowling the Malacca Strait may be part of a syndicate that can either have links to the crew on board the hijacking target or inside knowledge about the ship and cargo.
Attacks by armed gangs on shipping in the Malacca Strait have ranged from 12 to 20 incidents a year over the last three years, says the Singapore-based Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia (ReCAAP).
