Flooding has forced the closure of some roads and highways in the South Island, while roofs have been damaged and flights cancelled in the North as severe weather lashes the country.
A "significant number" of people in Nelson have now chosen to evacuate, according to Nelson Tasman Civil Defence.
"While we did assist some people from their homes there have been a significant number of people who have felt uncomfortable enough that they've self-evacuated," information manager Paul Shattock said.
Smaller rivers were a major area of concern.
"Our larger rivers seem to be coping quite well, it's some of the smaller rivers because the ground is so saturated if we have any localised downpours then those smaller streams and rivers could rise very rapidly and lead to further floods.
"The Wai-iti is probably one of the rivers they're looking at most closely at the moment, it seems to be running very high."
Meanwhile, Auckland Airport said 21 flights have been cancelled and 11 flights have been delayed - mostly impacting flights to or from regional destinations.
The severe thunderstorm warning has since been lifted for Auckland, but the same warning has been issued for other parts of the North Island as the wind and rain makes its way down.
A number of state highways and roads at the top of the South Island are closed, with a state of emergency has been declared for Nelson and Marlborough as a result of severe weather and evacuations.
Photo: Kate Green
Tasman District Council says the declaration will allow agencies to rapidly respond, with slips and flooding across the district and further rain forecast. Motorists are being asked to avoid travelling due to other road closures.
Earlier on Friday a section of road in Auckland's Blockhouse Bay was closed after wind blew the roof off a commercial building and partially collapsed the front of the structure.
Power lines near the damaged building were also down, with half-a-dozen fire appliances deployed to the site.
