The Ministry of Health says regions that avoided swine flu last year are likely to be worst hit this winter.
Updated figures are due to be issued on Thursday, but the ministry says there has been a marked increase in flu-like and other respiratory illnesses among patients.
Public Health Director Mark Jacobs says the Bay of Plenty, Lakes and Taranaki District Health Boards had lower rates last year and are already reporting more hospitalisations.
As of last week 158 people have been admitted to hospital this year with the H1N1 influenza and two people have died.
Dr Jacobs encourages people to get a flu injection and says there are still 15,500 doses of seasonal vaccine left.