Health Minister Tony Ryall says it is inevitable that swine flu will spread, possibly hitting up to a third of the population, but people should not be alarmed.
New Zealand would continue its tight containment approach in light of yesterday's World Health Organisation declaration of a pandemic.
"Our message is don't be alarmed. New Zealand is going to carry on the way that we have and we will keep people fully informed of any changes that need to be made," Mr Ryall told Radio New Zealand.
He did not think New Zealand needed to change its response.
"We are running a very tight containment strategy and it's working well." Mr Ryall said it was inevitable the flu would spread.
"Numbers are going to continue to rise and that's why it's important that anyone who develops flu-like symptoms stays away from work, stays away from school because that's how it will be spread -- if people who have got it are out there coughing and spluttering." The ministry had done projections on how bad things could get.
"The upper level is of course you might end up with 20 or 30 percent of the population with swine flu, but we don't know and that's why New Zealand is running its very tight containment strategy, it's working well for New Zealand." Mr Ryall emphasised the WHO decision was about international spread of the illness, not severity. Cases in New Zealand were no worse than the normal winter flu.
He said it was important to contain the flu as much as possible or health services could become overloaded.
"Every day we can keep swine flu from wider community spread in New Zealand is another day that we are not putting more and more pressure on our emergency departments and GP clinics because we are just about to enter the normal winter seasonal flu period." General practitioners are preparing to face the issue and have requested improved access to protective masks, gloves and gowns to enable them to treat patients who may arrive at their practices with swine flu.
Medical Association chairman Peter Foley said only some district health boards had released funds to ensure general practices remained fully stocked with supplies.
Doctors have predicted major challenges in the early stage of the pandemic would be protecting health workers from the virus and educating the public about self-protection.
Though regional medical officers of health will have the power to close borders, restrict public gatherings, put patients in isolation and shut schools and workplaces, the Ministry of Health has said its response to the pandemic will depend on the local situation.
Last night the number of confirmed cases of swine flu rose to 27, with 10 of them still being treated with Tamiflu in isolation. The rest have recovered. There are another 10 "probable" cases awaiting confirmation.
Ministry of Health chief public health advisor, Dr Ashley Bloomfield, has predicted that as more people test positive for swine flu more workplaces, schools, and childcare centres will be affected.
Seasonal flu hits up to 20 percent, about 760,000 New Zealanders each year. On average, 2.7 percent of the population (156,000 people) will go to their GP because of flu each year and an estimated 95 people will die.
Treasury estimates in 2007 of the economic impact in New Zealand of a flu pandemic ranged from a 10 percent drop in Gross Domestic Product (GDP) for an epidemic of a severe form, to a fall-off of between 1 percent and 2 percent for a relatively benign virus.
But acting assistant Treasury Secretary Colin Hall has said those figures have probably been overtaken by the global recession.
