A 43-year-old woman from Timaru is the 20th New Zealander to die with swine flu, after battling it for three months.

The Ministry of Health says it was advised of the death on Wednesday. The woman was in an intensive care unit in Auckland.

Deputy director of public health Dr Fran McGrath says swine flu is still a risk.

"While for the majority of people it's a moderate illness, or even a very mild illness, there are some people for whom it can develop into a very severe illness and it can develop quite quickly."

Dr McGrath says the woman's family has asked health officials not to release any more information about her death.