Flight TM470 took off from Maputo at 1456 IST yesterday and had been due to land in the Angolan capital Luanda at 1840 IST, but never arrived, the airline said in a statement.
"Initial information suggests it might have landed in Rundu, in northern Namibia near the border with Botswana and Angola."
"LAM airlines, aeronautical and airport authorities are trying to establish contact to confirm the information," it added.
Company spokesman Norberto Mucopa could not confirm the nationalities of the people on board nor the time of the last contact with the Brazilian-produced Embraer 190.
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Mucopa declined to comment on reports the plane went down in a storm.
"The last contact was in the north of Namibia," he told AFP.
A police commander confirmed the incident to AFP in Namibia.
"We are busy searching. It's dark now and it makes our job a bit difficult," said Olavi Auanga, police commander of the Kavango West region, where the control lost signal with the aircraft.
An aviation officer in the area told AFP on condition of anonymity that unconfirmed reports suggested the airplane may have gone down in the Bwabwata National Park around 200 kilometres east of Rundu.