New Zealand immigration authorities say a man who skipped Perth's COVID-19 lockdown to fly to Auckland "has a case to answer".
The man made use of the trans-Tasman bubble on Monday to fly quarantine-free into Auckland and on to Northland, where he is now self-isolating.
The travel appears to breach the conditions of both Western Australia's lockdown and the trans-Tasman travel regime introduced last week.
Immigration New Zealand manager Peter Elms said the man left Perth during the lockdown, but the failure to detect him prior to leaving the airport was not his organisation's mistake.
"The first time we were aware ... was when he arrived in Auckland," he told Radio NZ.
"We don't have visibility of all of the traveller movements in Australia.
"As soon as we became aware of that we took steps to notify the Ministry of Health."
Mr Elms confirmed INZ's intervention came only after the man had left the airport.
Another 73 people were blocked from entering New Zealand from Perth, according to INZ, but the man changed his travel itinerary which made his movements hard to detect.
"This person has a case to answer," Mr Elms said, confirming an investigation had begun into the breach.
In a statement on Tuesday, the health ministry said the public health risk was low.
"It serves as an important reminder that our public health response relies on accuracy and people fully complying with the safety measures that have been put in place by both countries," it said.
"The actions of one person could jeopardise quarantine-free travel with Australia for everyone."
NZ paused travel from Western Australia from Saturday to Monday in light of Perth's three-day lockdown.
Late on Tuesday, COVID-19 Minister Chris Hipkins said New Zealand would lift its ban on arrivals from Perth as of midday on Wednesday.
"The government is satisfied the risk is low, based on the advice of the Director-General of Health, and that the trans-Tasman Bubble is working largely as planned," he said.