PUTRAJAYA (THE STAR/ASIA NEWS NETWORK) - Missing oil tanker MT Orkim Harmony is most likely near Indonesia's Natuna and Anambas Islands in the South China Sea, said Malaysian Vice-Admiral Datuk Ahmad Puzi Ab Kahar.

The vessel could be in Vietnamese waters if it had headed north based on its last known speed and position, said the Malaysian Maritime Enforcement Agency (MMEA) deputy director-general.

"If it had headed east, it would be in Kota Kinabalu waters. But until now, we have not been able to track it in Sabah and Sarawak waters.

"So, there is a big possibility that it is still in the South China Sea and nearby areas," he told reporters at the MMEA headquarters here in Putrajaya on Monday.

"The biggest possibility is that the ship is near the Natuna and Anambas Islands."

Admiral Ahmad Puzi said the agency had contacted the Indonesian authorities to assist in the search and ask for permission to enter their waters to search for the tanker.

He added that the tanker was likely a case of piracy for economic gains.

The tanker was carrying 5,879 tonnes of RON95 fuel belonging to Petronas worth RM21 million (S$7.5 million).

Responding to questions on whether the ship's 22-member crew had been taken hostage, Admiral Ahmad Puzi said no ransom demand had been made as of Monday.

The crew comprised 16 Malaysians, five Indonesians and one Myanmar national.

Admiral Ahmad Puzi said that while past maritime robberies saw fuel cargo such as automotive diesel oil being siphoned off to other ships, the RON95 petrol carried by MT Orkim Harmony would be harder to transfer as it was highly flammable.

"We believe the ability to receive the fuel in the nearby islands is not available. The culprits could be looking for those who can receive the fuel," he said.

Admiral Ahmad Puzi said the tanker left Malacca on Wednesday and was scheduled to arrive at Kuantan port 10.30am the next day, but communication was lost at about 8.57pm.

He added that MMEA was notified at about 6.30am on Saturday.

The ship's last known location was 30 nautical miles off Tanjung Sedili.