A Malaysia Airlines flight carrying 227 passengers and 12 crew crashed in the South China Sea on Saturday, Vietnamese state media said, quoting a senior naval official.
The Boeing 777-200ER flight from Kuala Lumpur to Beijing had been missing for hours when Vietnam's Tuoi Tre news quoted Admiral Ngo Van Phat as saying he had asked boats from an island off south Vietnam to rush to the crash site.
If the report is confirmed, it would mark the U.S.-built airliner's deadliest crash since entering service 19 years ago.
Malaysia Airlines had yet to confirm that the aircraft had crashed. It said earlier in the day that no distress signal had been given and cited early speculation that the plane may have landed in Nanming in southern China.
Flight MH370, operating a Boeing 777-200ER aircraft, last had contact with air traffic controllers 120 nautical miles off the east coast of the Malaysian town of Kota Bharu, Malaysia Airlines chief executive Ahmad Jauhari Yahya said in a statement read to a news conference in Kuala Lumpur.