A traveller from the Cook Islands has breached the trans-Tasman travel bubble by flying to Perth from Auckland today.
Under the trans-Tasman bubble arrangements, travellers must spend at least 14 days in New Zealand prior to departure.
In a written statement, Air New Zealand confirmed it had been made aware that a passenger on board flight NZ175 was ineligible for quarantine-free travel to Australia.
A spokesperson said the airline was working with the relevant authorities on both sides of the Tasman and would follow their guidance.
Any decision over what happens to this passenger is now in the hands of the authorities in Western Australia.
Immigration New Zealand border manager Peter Elms said officials only became aware the New Zealand citizen was ineligible to travel during "routine checking" shortly after the flight left.
More than 50,000 people have travelled between New Zealand and Australia since trans-Tasman quarantine-free travel arrangements were put in place on 19 April.
Meanwhile people arriving in New Zealand from Brisbane are being asked to monitor their health for the next 14 days, after a reported green zone breach at Brisbane Airport.