A rare tornado has swept through New Zealand’s largest city Auckland killing three people and forcing 250 more to leave their homes.

Seven people are being treated in hospital in Auckland after the tornado struck at lunchtime.

Local media reports say two of the dead were killed when a concrete slab landed on a truck.

The twister hit Hobsonville and Whenuapai, western suburbs of Auckland, uprooting trees, damaging buildings and causing flooding that closed roads.

It is believed some of the victims were working on a building site constructing a new school when the freak weather system struck.

Around 150 homes have been damaged and residents are being housed at an air force base.

Shaken builder Sam Nuthall, who was working at the school site, said he saw big dark clouds and thought it would just be a rainstorm, but was then forced to shelter between a block wall and a truck.

“You couldn’t see it coming … there was debris flying everywhere, steel getting thrown around,” he told Radio New Zealand.

There were 50 to 80 people on the site after the tornado struck he said.

Whenuapai resident Suzanne McFadden told 3News it was “five minutes of utter devastation”.

“It got very muggy, very still. Suddenly the sky went very, very black, almost like night, and a huge wind came across the river,” she said.

“It ripped century-old pine trees out of the ground, it’s taken roofs off houses, it’s crushed cars and boats.

“The main street of our village looks like a bomb’s gone off and we’re all very aware that it could turn around and another one could strike.”

Auckland Council spokesman Glyn Walters said some of the homes that were hit had roofs torn off or were severely damaged while others had more minor damage or had lost power.

The worst weather appeared to have passed by mid-afternoon, Walters said. “It’s clearing slightly but people need to be careful out there,” he said.

New Zealand’s Prime Minister John Key, whose electorate covers the damaged area, extended his sympathy to friends and family of the victims.

Some flights in and out of Auckland Airport had been delayed or cancelled and some local bus services stopped.

Loretta Radich arrived at her business on Hobsonville Road just as the storm hit.

“We saw the rain going in all different directions and the windows were flapping,” she told the AAP news agency.

Government forecaster MetService is warning of the likelihood of possible tornadoes and thunderstorms as the weather front heads south to the Bay of Plenty.

Watch New Zealand deadly Tornado

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