Health Minister Tony Ryall says it is inevitable that swine flu will spread widely - possibly infecting as many as a million New Zealanders.
People are being encouraged by health experts to get immunised against normal winter flus so they do not suffer a "double whammy" as New Zealand maintains its tight containment approach following yesterday's World Health Organisation declaration of a pandemic.
The WHO made its decision because the spread of the flu but Mr Ryall emphasised cases remained mild.
New Zealand confirmed cases have passed 30, with details to be revealed this afternoon.
So far cases cases have related to travel rather than infection in the community.
Tamiflu stocks were good, with doses issued for containment, though that could change when the virus spread more widely, Mr Ryall said.
"It's inevitable with the increasing number of international cases of swine flu that we will end up with higher numbers in New Zealand and greater spread in the community," Mr Ryall told a press conference.
The pandemic could last up to two years and see 30 percent of the population -- around a million people -- infected.
Deputy director for Public Health Dr Darren Hunt said people were not immune to the virus because it was new and the estimates were not surprising.
"It becomes dangerous for people who would normally be susceptible to the flu, people that may have chronic underlying conditions or other reasons... the reason that we are particularly concerned is simply because of the numbers that may be infected." He urged people to be vaccinated against winter flus -- "so they don't get a double whammy."
The additional load on health services would come on top of normal winter flus and staff would also get sick. An Auckland nurse and her son have the swine flu.
Medical Association chairman Peter Foley today said only some district health boards had released funds to ensure general practices remained fully stocked with supplies such as masks and gowns.
Mr Ryall said the focus on containment aimed to keep as short as possible the period that health services were put under pressure.
Dr Hunt said the virus had spread in Australia and would do so in New Zealand.
The WHO was working with partners on a vaccine and New Zealand was making efforts to obtain it once available.
Dr Hunt was asked about the Maori hongi and other physical contact spreading flu.
He said sick people should avoid physical contact. People should take health precautions and stay home if they were ill.
Mr Ryall said there were no plans to look at compensation for businesses where staff were quarantined at this stage.
Unions had called for assistance for employers to keep paying quarantined workers.
Regional medical officers of health will have the power to close borders, restrict public gatherings, put patients in isolation and shut schools and workplaces.
Mr Ryall said there had not been an issue so far and there could be changes to quarantine and isolation rules as things changed.
Seasonal flu hits up to 20 percent, about 760,000 New Zealanders each year, and an estimated 95 people die annually.