Qantas is investigating what caused a plane travelling from Adelaide to Melbourne on Tuesday morning to lose pressure mid-flight.
The Boeing 737 was carrying 99 passengers and landed safely at Melbourne airport just before 8am local time.
Passengers on board flight QF670 say a sudden drop sparked panic before pilots requested a "rapid descent", the ABC reports.
Qantas says the landing was routine and no one needed medical assistance.
A spokeswoman says the airline is awaiting confirmation that the scare was caused by the plane's air conditioning system.