The 7,301-dwt Orkim Harmony (built 2009) and its crew are currently on the way back to Kuantan in Malaysia on Friday.
Reportedly, the perpetrators managed to escape and the authorities were tracking their whereabouts, said the Singapore-based Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia (ReCAAP) Information Sharing Centre.
On Thursday Malaysian authorities had said they were shadowing the vessel and were trying to persuade the hijackers to surrender.
State news agency Bernama, quoting Malaysia's naval chief Admiral Abdul Aziz Jaafar, said the pirates had repainted the ship and changed the name to Kim Harmon.
The Malaysian-flagged Orkim Harmony lost communication with its owners last week and is believed to have been hijacked.
The tanker left Malacca last Wednesday and was due to arrive at Kuantan port early the next day, but communication was lost just before 9pm local time.
However, Malaysian authorities were not notified about its disappearance until first thing Saturday morning.
The ship was reportedly carrying 5,879t of RON95 fuel worth MYR 21m ($5.5m) which belongs to state-owned oil company Petronas.
The ship also had a crew of 22 people made up of Indonesians, Malaysians and Myanmar nationals.
It was the second Orkim Ship Management-controlled vessel to have been attacked by pirates in the space of eight days.
The 7,119-dwt Orkim Victory (built 2009) was hijacked and had its cargo of fuel siphoned off and stolen in the early hours of 4 June 2015.
