The long-haul, low-cost Malaysian airline confirmed the diversion but did not say how many people were on board the flight.
"AirAsia X would like to confirm that flight from Sydney to Kuala Lumpur was diverted to Melbourne due to a technical issue.
"The diversion is in compliance with all international aviation safety guidelines and landed safely in Melbourne," said the airline in a statement, denying reports that it was an emergency landing.
"Upon completion of all necessary safety inspections, the said aircraft departed Melbourne and is expected to arrive into Kuala Lumpur at 10.21pm (local time)," it said.
The airlines fixed the plane before it took off for Kuala Lumpur about four hours after landing.