The twin-jet Boeing 738 landed at Sydney Airport from Auckland, New Zealand.
Multiple outlets reported it had an engine failure.
New South Wales Ambulance had confirmed its paramedics were responding to the mayday alert.
"Paramedics have been called," the ambulance service spokeswoman had said as Flight QF144 from Auckland approached the airport.
Australia's Channel Nine television news said there were "reports of an engine failure".
FlightRadar had indicated the flight was over the Pacific Ocean at the time of the mayday alert.
A mayday call is issued when a flight is in grave and imminent danger and needs immediate assistance, according to Airservices Australia.