Emergency services rushed to the aircraft as it landed at Sydney Airport on Wednesday afternoon.
QF144 from Auckland issued the distress call after an in-flight emergency when the plane suffered an engine failure, AAP understands.
A Qantas spokesperson told ABC the flight experienced an issue with one of its engines about an hour from its destination.
"While a mayday was initially issued it was downgraded to a PAN - Possible Assistance Needed," ABC News reported.
After the aircraft landed, two yellow airport fire appliances drove out to escort it to a park spot.
NSW Ambulance confirmed its paramedics responded to a mayday alert issued by the flight from Auckland to Sydney.
Federal Transport Minister Catherine King lauded the airline's safety record after a brief scare that had 100,000 people tracking the flight online.
"A relief to know that QF144 has landed safely," she tweeted.
"Well done to the highly experienced crew for getting the plane safely home.
"Australia's aviation industry is among the safest in the world because of the dedicated staff working on planes and behind the scenes".
FlightRadar indicated the 10-year-old, twin-jet Boeing 737-800 plane travelling was over the Pacific Ocean when the call was issued.
"A mayday call is an internationally recognised, emergency or distress call," a spokeswoman for the Australian Maritime Safety Authority told AAP.
The call is issued when a flight is in grave and imminent danger and needs immediate assistance, according to Airservices Australia.
Once the call is issued controllers alert aviation rescue, firefighting and emergency services with details on how to respond. They also provide assistance to pilots.
"As a precaution Sydney Airport had emergency crews on stand-by including firefighters, ambulance and police," a spokesperson told AAP.
Aviation expert Neil Hansford told Sky News that "Qantas has never had a passenger lost on a jet aircraft in its history".
"What you may well find when the aircraft lands is that it may be prudence, rather than an uncontrollable situation."
Mr Hansford said Boeing 737s can fly and land on only one engine.
24°C