Australians are among the 227 passengers on board a Malaysia Airlines flight that has gone missing in Asia.
Malaysia Airlines spokesman Lincoln Lee confirmed there were multiple Australian passengers on the Beijing-bound
Boeing 777 aircraft that lost contact with air-traffic control after departing Kuala Lumpur.
"We can confirm there were Australian passengrers on board the aircraft. We cannot say how many," Mr Lee said.
Search and rescue teams are trying to find the plane. The airline lost contact with the B777-200 aircraft after it departed Kuala Lumpur shortly after 12.40am local time on Saturday.
It was expected to land in Beijing at 6.30am.
Flight MH370 was carrying 239 people, including two infants and 12 crew members.
Malaysia Airlines said in a statement that it was working with the authorities who have activated their search and rescue team to locate the aircraft.
An unconfirmed report from a flight tracking website said the plane had plunged more than 200 metres and changed course in the last minute that it had transmitted data.
The airline will provide regular updates on the situation.
Australian authorities are trying to confirm whether there were any Australian passengers on board the missing flight, a spokeswoman for the Department of Foreign Affairs and Trade said.
Chinese authorities have reportedly said the flight never entered Chinese airspace.
A flight-tracking website said communication was lost 20 minutes after departure from Kuala Lumpur.
"It doesn't sound very good," retired American Airlines captain Jim Tilmon told CNN on Saturday.
He said that the route was mostly overland, which meant that there would be plenty of radars and radios to contact the plane.
"I've been trying to come up with every scenario that I could just to explain this away, but I haven't been very successful."
He said the plane was "about as sophisticated as any commercial airplane could possibly be".
Some websites listed the plane as having landed at 6.10am in Beijing but Malaysian Airlines issued the statement to report it was missing at 7.54am.
The missing plane is believed to have been involved in a crash in August, 2012, when it damaged the tail of a China Eastern Airlines plane at Shanghai Pudong Airport, according to unconfirmed reports.
In the incident, the tip of the wing of the Malaysia Airlines Boeing 777 broke off.
Malaysia Airlines has just released a statement saying its "thoughts and prayers" were with all the passengers on board the missing plane, and their families.
Passengers of 13 nationalities were on board the plane.
"[The] focus of the airline is to work with the emergency responders and authorities and mobilize its full support," chief executive Ahmad Jauhari Yahya said.
"Our team is currently calling the next-of-kin of passengers and crew."
Malaysia Airlines is the national carrier of Malaysia and one of Asia's largest, flying nearly 37,000 passengers daily to some 80 destinations worldwide.
The airline said the public can call +60-378841234 for information about the plane.
Licenced pilot John Preston said that rumours that the aircraft has made an emergency landing in Nanming are unlikely.
"I think we can safely discount that."
He said Chinese authorities had confirmed the plane had not entered their airspace. He said there were several ways for the aircraft to communicate with the authorities but that does not appear to have happened.
China's state-run news agency Xinhua reported the plane was lost in airspace controlled by Vietnam, and did not make contact with Chinese air traffic controllers. China is assisting the airline in its search for the plane, Xinhua said. There were no storms in the area of the South China Sea where the plane was flying across. The weather was generally fine with light clouds.
Malaysia Airlines denied reports circulating on the internet the plane had landed safely in Nanjing China. "It's not true. We don't know where the plane is now," said Fuad Sharuji, from the the airline's operation control centre. Mr Fuad confirmed contact was lost two hours into its six-hour flight. The pilots made no distress call.
The plane was travelling at 35,000 feet when contact was lost.Its pilots had made contact with air traffic control in the Vietnamese city of Ho Chi Minh. Malaysia Airlines' Vice President of operations told CNN that no distress call or problems were reported from the aircraft prior to its disappearance. The plane was reportedly flying at 35K feet at the time.The airline was due to hold a press conference at 11am Kuala Lumpur time.
The plane had enough fuel to fly for seven hours, one hour more than the flight time to Beijing.
Anyone wanting more information on the flight should call the airline on +60-378841234.