More than 60 pre-school and secondary students are in isolation after two Christchurch children tested positive for swine flu.
The number of confirmed cases of the virus in New Zealand rose to 36 on Friday.
Canterbury's medical officer of health Ramon Pink says the two children, aged four and eight, are believed to have caught swine flu from their grandmother who returned from the Australian state of Victoria earlier this month.
Mr Pink says 18 children who had contact with the younger child at preschool are in isolation, and seven are showing flu-like symptoms.
The children's teenage brother is also being tested for the virus. He has been in contact with about 50 students and teachers from Burnside High School, who are also in isolation.
The Ministry of Health estimates more than one million New Zealanders could contract the virus, which the World Health Organisation on Thursday declared a pandemic.
The influenza pandemic declaration relates to the geographical spread of the disease, not its severity.
District councils say they have plans in place to keep essential services running in case of swine flu affecting large numbers of people.
Gisborne District Council chief executive Lindsay McKenzie says the council is using its planned response to bird flu as a basis for preparing for the swine flu pandemic.
He says residents of small towns should not consider themselves to be at lesser risk from the spread of swine flu.
Timaru District Council emergency management officer Lamorna Cooper says lessons have been learned from a national civil defence exercise two years ago.
Ms Cooper says the council is working with neighbouring districts to ensure help can reach isolated communities during a pandemic, though people in remote areas should still make plans to manage by themselves at home.
Far North District Council spokesperson Alison Lees says the council is also drawing on its experiences of civil defence emergencies during flooding.