HANOI (REUTERS) - A missing Malaysia Airlines (MAS) plane carrying 239 people "could have" crashed into Malaysian maritime territory, based on calculations provided by Malaysian rescue authorities, a Vietnam navy officer said on Saturday.

Admiral Ngo Van Phat told Reuters the plane may have crashed in Malaysian waters, 153 miles off the coast of Vietnam's Tho Chu island, according to its speed and last known location.

The admiral denied earlier reports in Vietnamese state media quoting him as saying the plane had actually crashed.

Tho Chu lies to the south-west of southern Vietnam and Phu Quoc Island, a popular tourist destination.

"Thai and Malaysian rescue teams would be better placed to conduct a rescue but Vietnamese navy boats in Phu Quoc island are ready to support any mission if requested," the admiral told Reuters.