Update -- 8 p.m.
China's state media say Vietnamese authorities have detected signals from the missing Malaysia Airlines plane.
The Xinhua News Agency, citing a local Vietnamese media report, says a Vietnamese search and rescue official reported that the signals have been detected from the plane from about 220 kilometres (120 miles) southwest of Vietnam's southernmost coastal province of Ca Mau.
Malaysia Airlines says its Boeing 777-200 carrying 239 people lost contact over the South China Sea early Saturday morning on a flight from Kuala Lumpur to Beijing.
Original story -- 6:45 p.m.
Malaysia Airlines said Saturday it lost contact with a plane carrying 239 people on its way from Kuala Lumpur to Beijing and search and rescue teams were trying to locate the aircraft.
Flight MH370 lost contact with the Subang air traffic control near Kuala Lumpur at 2:40 a.m. Saturday (18:40 GMT Friday).
According to China's state news agency, the plane lost communication over Vietnam with control department in Ho Chi Minh City at 1:20 a.m. The radar signal also was lost, Xinhua reported.
The flight was operated on the Boeing 777-200 aircraft. It departed Kuala Lumpur at 12:41 a.m. Saturday (16:41 GMT Friday) and was expected to land in Beijing at 6:30 a.m. Saturday (22:30 GMT Friday).
The plane was carrying 227 passengers, including two infants, and 12 crew members, the airline said.
The airline said it was working with authorities who activated their search and rescue team to locate the aircraft. The route would take the aircraft from Malaysia across to Vietnam and China.
"Our team is currently calling the next-of-kin of passengers and crew. Focus of the airline is to work with the emergency responders and authorities and mobilize its full support," Malaysia Airlines CEO Ahmad Jauhari Yahya said in a statement.
"Our thoughts and prayers are with all affected passengers and crew and their family members," he added.
Malaysia Airlines has 15 Boeing 777-200 jets in its fleet of about 100 planes. The state-owned carrier last month reported its fourth straight quarterly loss.
The 777 had not had a fatal crash in its 20 year history until the Asiana crash in San Francisco in July 2013.