A child who returned to New Zealand from North America on Sunday is this country's latest confirmed case of swine flu.
The Ministry of Health says the child, whose age is not disclosed, is in isolation and being treated.
The child was a passenger on Air New Zealand's Flight NZ1.
Other passengers on the flight are being contacted.
The ministry says 10 cases of swine flu have been confirmed in New Zealand.
Warning schools may be closed
Schools are being warned they could be forced to shut if students test positive for swine flu.
The Ministry of Health is sending letters to all schools on Tuesday, warning of possible closures of up to a week where cases of the illness are found.
There have been some school closures in Victoria and Queensland, with the number of confirmed swine flu cases in Australia now above 400.
The Health Ministry's Director of Public Health Mark Jacobs says the letter includes hygiene advice on preventing the spread of illness and a warning that confirmed cases could lead to school closures.
He says schools will have to plan on how to quickly notify parents of closures, as well as what options there are for continuing lessons, possibly using the internet.
Dr Jacobs says it is only a matter of time before more cases emerge in New Zealand.
Rangitoto College principal David Hodge says it would be hugely disruptive if schools were forced to close.
Cases of swine flu were diagnosed among a group of students at the school in May.
Mr Hodge says closing schools would be hard on working parents and students, especially those sitting major exams such as NCEA.