Vietnamese authorities say the last detected signal from a missing Malaysia Airlines flight from Kuala Lumpur to Beijing was above an area about 240 kilometers off the coast of Vietnam's southwestern Tho Chu island.
A Vietnamese naval commander has told state media that the missing plane carrying 239 passengers and crew could have crashed in Malaysian waters.
Admiral Ngo Van Phat said Saturday that Thai and Malaysian rescue teams would be better placed to search the area, but Vietnamese navy boats are ready to support the mission.
However, Malaysian acting Transport Minister Hishamuddin Tun Hussein told a news conference that he had not been informed that the plane had been located and no wreckage has been sighted.
The airline said it lost all contact with Flight MH370 about two hours after it took off from the Malaysian capital early Saturday morning local time.
At a news conference Saturday, Malaysia Airlines CEO Ahmed Jauhari Yahya said the airline is working with search and rescue teams to locate the aircraft and is calling the families of the passengers and crew.
The company's Facebook page said the passengers represented 14 different nationalities, including 152 Chinese, 38 Malaysians and four Americans.
China's official Xinhua news agency says contact with the Boeing B777-200 was lost in Vietnamese airspace. It says the plane never entered China's air traffic control area. Beijing said it has dispatched at least two rescue vessels to take part in the search.
The most recent accident involving a Boeing 777 was the Asiana Airlines crash at the San Francisco International Airport in July, 2013, in which three people died. Pilot error is suspected in that incident.