The last communication received from a Malaysia Airlines plane suggests everything was normal on board minutes before it went missing over the South China Sea, Malaysian authorities say.

Flight MH370 replied "All right, roger that" to a radio message from Malaysian air control, authorities said.

The search has been widened to waters off both sides of the peninsula.

Malaysia's air force chief has denied reports the plane was tracked to the Malacca Strait in the west.

The China-bound plane went missing on Saturday with 239 people on board.

It vanished about an hour after it took off from Kuala Lumpur International Airport, as it flew over the South China Sea, south of Vietnam's Ca Mau peninsula. No distress signal or message was sent.

Malaysian authorities revealed the plane's last communication at a news conference held in Beijing for relatives of the 154 Chinese who are among the missing passengers.

As the plane reached the boundary between Malaysian and Vietnamese airspace, the Malaysian air control announced it was handing over to Ho Chi Minh City Control.

Minutes later, all contact with Flight MH370 was lost.

China's foreign ministry said there was "too much confusion" regarding the information released about the plane's flight path.

"It is very hard for us to decide whether a given piece of information is accurate," spokesman Qin Gang told reporters in Beijing.

马方：失联发生在马方将管制交接给胡志明市管辖区域。

失联前马方最后一次联络内容：“已把你们(mh370)交接给胡志明市管辖区。”

MH370航班：“好的，收到。”

失联前MH370未有任何通报飞机出现异常，雷达扫描不到飞机编号信息，但仍能跟踪到空中有物体在飞行，几分钟飞行物体的信号消失。

可能出现的情况包括驾驶员主动关掉信号被劫机或无线电失灵、飞机解体。