Infographics on Swine Flu
"While some countries have seen H1N1 virus decline or crowded out by other strains, this is not the case in New Zealand," the deputy director of public health, Darren Hunt, said.
Four people are believed to have died from swine flu in New Zealand this year.
Hunt said there had been "significant outbreaks" in some areas of New Zealand, which had resulted in high levels of absenteeism from work and school and higher than normal hospital admissions.
"The pandemic influenza strain is the predominant strain circulating this winter," he said.
"We are seeing higher levels of hospitalisation in areas that weren't severely affected last year.
"To date, there had been over 300 people admitted to hospital this year with confirmed H1N1, which includes over 30 people admitted to intensive care."
WHO Director General Margaret Chan told a telephone news conference from Geneva that H1N1 had "largely run its course".
"The world is no longer in phase six of the pandemic alert. We are now moving into the post-pandemic period," she said.
The WHO's top flu official, Keiji Fukuda, said the influenza virus was no longer considered capable of causing another pandemic, even if more severe outbreaks might occur in some countries.
Swine flu has killed more than 18,449 people and affected some 214 countries and territories since it was uncovered in Mexico and the United States in April 2009, according to WHO data.