The plane lost contact in Ca Mau province airspace before it had entered contact with Ho Chi Minh City air traffic control," a statement posted on the official Vietnamese government website said.
The plane was meant to transfer to Ho Chi Minh City air traffic control at 1722 GMT but never appeared, the statement said, citing a senior Ministry of Defence official.
Vietnam's Ministry of Defence has launched rescue efforts to find the plane, working in coordination with Malaysian and Chinese officials, the statement added.