Houses have been evacuated after a tornado swept through the Kapiti Coast, north of Wellington, on Saturday afternoon between Waikanae and Peka Peka.
A woman was taken to Wellington Hospital in a serious condition with spinal injuries after an uprooted tree crushed the caravan she was in.
The ambulance service says two others were taken to a medical centre in Paraparaumu with minor injuries.
The police say the tornado struck between Waikanae and Peka Peka at about 4pm, tearing rooves off buildings and blowing cars off the road.
A Radio New Zealand reporter at the scene said Huia Street, which runs parallel with State Highway One at Waikanae, had been badly hit.
She says the northern part of the street has been evacuated because of the danger from fallen powerlines and damaged trees.
The tornado initially crossed State Highway 1, blowing a van onto its side, injuring the driver.
It then roared up a nearby hill, stripping trees bare, overturning residents' cars and tearing roofing iron from barns, throwing it around Huia Street.
Traffic, which was stalled for about two hours on the state highway, is moving again and contractors are clearing up the mess.
Firefighter John Arthur says he saw a large amount of damage.
"There was one car on its side lying in a ditch and there were three other cars which had a fair bit of damage.
"The big, historic woolshed was quite badly damaged and I could see another building, possibly a shed, had been demolished."
One resident said a house had been "flattened".
Line of thunderstorms
MetService says the severe weather on the Kapiti Coast was a result of a line of thunderstorms.
It says while the front has weakened, strong northwesterlies and more thunderstorms are expected in the area overnight.
There have also been reports of hail particularly around the Hutt Valley and Kapiti Coast.
Metservice forecaster Chris Noble says large parts of the country are also in for severe gales, heavy rain and hail.