The Health Ministry's principal medical adviser says some hospitals' intensive care units have reached their full capacity.
The comment comes as New Zealand researchers suggest swine flu is more infectious than first thought.
Principal medical adviser David Galler says some ICUs are already at capacity and some people who have become seriously ill after getting swine flu have been prioritised over non-urgent surgery.
Dr Galler says New Zealanders can be reassured that health services are continuing to provide quality care despite the increasing pressure on family doctors and hospitals from the rising number of swine flu cases.
Wellington's head of intensive care Dr Peter Hicks says the pressure is easing there, but Canterbury says it is feeling the strain and may use the private sector for some patients to help ease the load.
Director of public health Mark Jacobs says there are 66 patients in hospitals with swine flu throughout New Zealand, including 25 in intensive care.
Dr Jacobs says there are 150 ventilators available nationally and extras could be found, but it is up to individual hospitals what they do if patient numbers build.
He says hospitals have ways of coping, including shifting patients to other areas.
Meanwhile, the number of deaths from swine flu in New Zealand remains at 13 - a drop from 14 reported by Chief Coroner Neil MacLean on Thursday.
Judge MacLean says one case has gone from being definitely linked to swine flu to a suspected link.
Virus more infectious than previously thought
New findings from researchers show the swine flu virus is more easily spread than first thought.
Researchers from the University of Otago based say this means up to 80% of the entire population of New Zealand could become infected.
Associate Professor Michael Baker says new modelling shows that, on average, every person who gets the H1N1 virus in New Zealand is creating two secondary cases.
The findings are published in the latest New Zealand Medical Journal.
Radio New Zealand's health correspondent says it had been assumed up to half of the population could get swine flu.
However, Dr Baker says that could reach 80%, with two-thirds showing symptoms.
