Ryall said a further three children, from Northcote College who also visited Mexico, have started developing symptoms.
The flu has killed up to 86 people in Mexico and likely sickened about 1,400 in the country since April 13.
The flu has spread far beyond Mexico's borders with 20 confirmed cases in five U.S. states and suspected cases in Canada, France, Britain as well as New Zealand.
Key told TVNZ that the plan set up since the 2003 bird flu scare meant New Zealand had good stocks of the Tamiflu vaccine -- about 1.4 million treatments and the single gateway into New Zealand via Auckland meant control was easier.
Options included people not being allowed onto Air New Zealand flights if they were ill and those who arrive at Auckland being sent by a doctor stationed there since 5:00 a.m. Monday for checks.
He urged people who suspect they may have the flu to see a doctor, for sick people to stay home and precautions like hand washing and covering mouths when sneezing to be taken.
The authorities will contact passengers from the same international flight as the Rangitoto College students who are believed to have caught the potentially deadly swine flu while in Mexico.
The students, teachers and their families were now in home quarantine for an unspecified period of time.
