A maritime watchdog agency says a Vietnamese tanker carrying gas oil has lost contact and may have been hijacked by pirates after leaving Singapore port almost a week ago.

The International Maritime Bureau says the ship's owner lost contact with the Sunrise 689 and its 18 crew members after the 4,000-ton tanker left Singapore en route to Vietnam on Oct. 2.

Noel Choong, who heads the bureau's piracy reporting center in Kuala Lumpur, says the ship was believed to have been hijacked and its communications equipment appeared to have been switched off or destroyed. He said Wednesday that the ship can't be detected by satellite.

Choong says this is 12th case of piracy since April in Southeast Asia, where tankers went missing and were later released after cargo was stolen.