A Malaysia Airlines (MAS) plane flying from Kula Lumpur to Beijing has lost contact with air traffic control two hours into the flight, setting off fears the Boeing 777 carrying 239 people might have crashed over Vietnamese air space.

Malaysia Airlines said flight MH370 lost contact with the Subang Air Traffic Control at 2:40am almost two hours before it was supposed to land in Beijing. As many as 160 passengers are believed to be Chinese nationals.

The airline said people from 13 different countries were on board the aircraft and it was trying to contact the relatives of the passengers.

The aircraft had departed from Kuala Lumpur at 12:21am (1621 GMT).

China's Xinhua news agency reported the aircraft lost radar contact over Vietnam. It said the aircraft did not enter the Chinese air space.

Malaysia Airlines said it was monitoring the situation and will give regular updates on its website. The airline is also expected to hold a press conference over suspected plane mishap shortly.

"The flight was carrying 227 passengers (including two infants), 12 crew members. Malaysia Airlines is currently working with the authorities who have activated their search and rescue team to locate the aircraft," the airlines said in a statement.

The airline said relatives and friends of the passengers in the missing plane can call 03-7884 1234 for information.

"Focus of the airline is to work with the emergency responders and authorities and mobilise its full support. Our thoughts and prayers are with all affected passengers and crew and their family members," MAS said.

This is the second incident involving a Boeing 777 in the span of a year after July's Asiana mishap at San Francisco airport which claimed three lives.

Boeing said in Twitter: "We're closely monitoring reports on Malaysia flight MH370. Our thoughts are with everyone on board."