A Malaysia Airlines plane with 239 people aboard, including four Americans, is missing after losing contact with air traffic control on its way from Kuala Lumpur to Beijing early Saturday.

The airline said in a statement it is working to locate the Boeing 777-200 after it lost contact with Subang Air Traffic Control at 2:40 a.m., two hours into the flight. It was scheduled to land in Beijing at 6:30 a.m.

China's state-run news agency Xinhua reported the plane was lost in airspace controlled by Vietnam, and never made contact with Chinese air traffic controllers. There have been no reports of a plane crashing into Chinese waters, and China is assisting the airline in its search for the plane.

The plane is carrying 227 passengers, including two infants, and 12 crew members. The airline said in a statement that the passengers are of 14 different nationalities and the airline is currently notifying next-of-kin about the situation.

"Our thoughts and prayers are with all affected passengers and crew and their family members," Malaysian Airlines CEO Ahmad Jauhari Yahya said.

Those aboard included 153 Chinese citizens, including one infant, 38 Malaysian citizens, 12 Indonesian citizens, seven Australian citizens, four American citizens, including one infant, two citizens each from New Zealand, Canada and Ukraine and one each from Russia, Italy, Taiwan, the Netherlands and Austria.

"We are extremely worried,'' Chinese Foreign Minister Wang Yi told reporters in Beijing. "We are doing all we can to get details. The news is very disturbing. We hope everyone on the
plane is safe."

Vietnamese website VN Express said a Vietnamese search and rescue official reported that signals from the plane were detected about 140 miles southwest of Vietnam's southernmost Ca Mau province. But a Vietnam rescue official denied that a signal had been detected.

"We have been seeking but no signal from the plane yet," Pham Hien, director of a Vietnam maritime search and rescue coordination center in Vung Tau, told Reuters.

Malaysia Airlines said it is working with authorities who have activated a Search and Rescue team to locate the plane. The route would take the aircraft from Malaysia across to Vietnam and China.

The airline says the plane's pilot is Captain Zaharie Ahmad Shah, a 53-year-old who has been with the airline for over 30 years. The plane's first officer is Fariq Ab.Hamid, a 27-year-old who joined the airline in 2007. Both are Malaysians.

At Beijing's airport, Zhai Le was waiting for her friends, a couple, who were on their way back to the Chinese capital on the flight. She said she was very concerned because she hadn't been able to reach them.

Airport authorities posted a written notice asking relatives and friends of passengers to gather to a hotel about 30 minutes drive from the airport to wait for further information, and provided a shuttle bus service.

Another woman wept aboard the shuttle bus while talking by mobile phone, " They want us to go to the hotel. It cannot be good!"

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 has not had a fatal crash in its 20 year history until the Asiana crash in San Francisco in July 2013.

Boeing said on its Twitter account it is monitoring the situation, and "our thoughts are with everyone on board."

In the US alone, between 1983 and 2000, there were 568 plane crashes. Out of the collective 53,487 people onboard, 51,207 survived.