Health officials in Auckland admit they overreacted after quarantining a flight from Japan carrying students who appeared to have the flu.
Some of the passengers have described the biosecurity alert as chaotic and embarrassing.
But the Auckland Regional Public Health Service says it has to take a stringent approach and treat such scenarios as potentially serious.
The Air New Zealand flight carrying 274 passengers arrived at Auckland Airport from Tokyo at 9.25am on Monday.
The Boeing 777-200 plane was cordoned off and health officials were called in after 73 Japanese home-stay students out a group of 90 had shown flu-like symptoms.
A spokesperson for the home-stay group says it appears there was an over-reaction.
A Medical Officer of Health, Richard Hoskins, says health authorities may have overreacted to the situation but that is a far better response than under-reacting.
Dr Hoskins says health authorities have a duty to take any precaution necessary to protect New Zealanders from new diseases.
He says all the students had already been immunised against seasonal influenza before leaving Japan. Some of them were found to have a common cold.
"In hindsight, yes, you would classify this as an over-reaction but we had a large group of people travelling into the country that we were notified of in good time, and we needed to take it seriously until we knew that it wasn't a significant new illness for New Zealand."
Dr Julia Peters, who headed the health service team, is defending the time it took to get on the plane.
PM backs reaction
Prime Minister John Key says health officials were right to act cautiously when they quarantined the plane.
Mr Key says he has not been fully briefed on the incident, but the response sounds like it was proportionate.
He says it sounds like officials acted cautiously until they knew what they were dealing with, which is the right approach.
Handling chaotic - passenger
A passenger on the flight says it was a chaotic scene, with health officials taking an hour-and-a-half to respond and begin medical assessments.
Lauren Borgas, who was at the back of the plane sitting near the students, told Checkpoint she was among those given a red sticker and taken to a quarantine room.
She says amazingly the Japanese students were given the all clear and allowed to mingle with the other passengers.
Ms Borgas says while the mix up was eventually discovered by an airport manager, the whole situation was chaotic and no one seemed to know what was happening.
She says she was embarrassed to be a New Zealander.