The MT Oriental Glory was hijacked late Tuesday in the South China Sea off southeast Malaysia, the navy said in a statement.
Pirates stole its gas oil cargo before setting it adrift with damaged communication equipment and engine, the statement said.
Noel Choong, head of the International Maritime Bureau's Kuala Lumpur-based Piracy Reporting Centre, warned of the increasing number of incidents in the area.
The ship, whose crew was unhurt, was travelling from Singapore to Sandakan in the Malaysian part of Borneo island.
"This is the ninth attack in these waters recently... It's a big concern," he said, urging ships to be vigilant so that pirates could not surprise them.
Earlier this month pirates hijacked a Singapore-managed tanker in the South China Sea, stealing part of its cargo and damaging its communication equipment.
The spate of attacks has raised fears that Southeast Asia's vital shipping lanes could once again become a hotspot for piracy unless countries in the area quickly step up patrols.
Regional cooperation to crack down on the menace has successfully curbed such attacks in the past.
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