Flight QZ535, bound for the Indonesian island of Bali, changed course about 25 minutes after take-off on Sunday.
The Airbus A320, carrying 151 people, landed safely at Perth Airport.
AirAsia said the flight experienced a "technical issue". Australian media said it had appeared to lose altitude.
"We were all pretty much saying goodbye to each other. It was really upsetting," one passenger told the local Nine network.
