An A330 Airbus was forced to make an emergency landing at Darwin Airport.
The plane was carrying dozens of army personnel on a flight to Kuwait when the cabin filled with smoke about 40 minutes into an eight-hour flight.
The private contractor operating the flight, Strategic Aviation, says the crew noticed a strong smell coming from the air-conditioning system; the problem is being investigated.
At least three people were taken to hospital as a precaution soon after the plane returned to Darwin.
Two months ago an A320 Airbus ploughed into the sea off southern France, for reasons yet to be established. All seven people aboard, including five New Zealanders, died.
Safety allegations made 18 months ago
Eighteen months ago, former Strategic Aviation employees made serious allegations to the Australian Broadcasting Corporation about the company's commitment to safety.
The company strenuously denied those allegations and defended its record.