HANOI, March 12 — Vietnam is sending a team to Vung Tau in the nation’s southeast after getting an e-mail tip from an oil rig worker about the missing Malaysian Air jet on the fifth day of a multi-nation search effort.

A person who said he spotted what appeared to be a plane on fire sent an e-mail to Vietnam government officials, Vo Van Tuan, deputy head of the national committee for civil aviation safety, said by phone.

Earlier this week a plane had alerted Hong Kong air traffic controllers about sighting metal debris in the sea near Vung Tau, the Civil Aviation Authority had said. The possible debris area is 60 kilometres southeast off the coastal city, Lai Xuan Thanh, chief of the country’s civil aviation agency, had said earlier.

Malaysia is widening the area being combed for signs of the plane — missing since March 8 — to include the Malacca Strait. That’s roughly in the opposite direction as the intended course of the Beijing-bound Boeing Co. 777-200 over the Gulf of Thailand.

The absence of wreckage has kept alive various theories about the plane’s disappearance, from an accident to hijacking to sabotage. The plane’s position when it vanished March 8 may be in doubt, said Richard Bloom, director of terrorism and security studies at Embry-Riddle Aeronautical University in Prescott, Arizona.

“When flying over water, in my opinion there is no such thing as 100 per cent accurate technology of any kind,” Bloom said in an interview. “Not all of that information may have been getting back. It could have been distorted by occurrences still to be determined.” — Bloomberg