A freak tornado hit New Zealand's largest city Auckland on Tuesday, killing one person and injuring dozens more as it ripped the roof off a suburban shopping mall.

Packing winds of 200 kilometres an hour (125 miles an hour), the twister hit the suburb of Albany without warning at about 3pm (0300 GMT), flipping cars and uprooting trees as it carved a trail of destruction stretching for kilometres.

Television footage showed huge pieces of roofing and wreckage flying through the air, sending panicked locals fleeing for their lives.

Witnesses said the tornado sounded like "a giant vacuum cleaner" when it tore across the Albany Megacentre, one of the largest shopping malls in the country.

"All we could see was a big black cloud spinning above it and debris flying everywhere," Samantha Davey, who works in the mall, told national radio.

Authorities initially reported two dead but later revised the toll down to one, with Auckland mayor Len Brown expressing amazement more were not killed, particularly considering the hundreds who died in recent US twisters.

"That there was a big, mean beast of a tornado... we're just extraordinarily lucky that there hasn't been more loss of life," he told TV3.

The tornado is the latest in a string of disasters to hit New Zealand, including two earthquakes in Christchurch, the second of which claimed more than 180 lives, and a colliery explosion last November in which 29 miners died.

Witness Rob Crawford said the shopping centre resembled a disaster movie after the tornado, which passed over in less than 30 seconds.

"Car parks scattered with the remains of trees, upturned cars. There's iron off the roof... it's surreal," he told the New Zealand Herald.

"It's a movie set. (You think) is this real, is this happening? But when you see people lying on the ground, covered in blood, clutching their heads, it's damn real."

Shopper Anita Campbell sheltered in the mall, emerging to discover the terrifying winds had lifted her car and tossed it more than 100 metres (330 feet) across the road.

"It's actually lifted it up and pulled it over the wall," she told TV3, surveying her wrecked vehicle.

Auckland city council activated its emergency response centre to help coordinate relief efforts, while police urged people to stay indoors.

"We encourage people to return home, contact family if necessary. Leave roads near Albany commercial area free for emergency services," police said.

Prime Minister John Key said he was closely monitoring the situation and would offer authorities in Auckland any assistance required.

"Obviously it's been a very powerful and quite devastating tornado that's caused a significant amount of damage in a very localised area," he told reporters.

New Zealand Metservice meteorologist Peter Kreft said the tornado hit without warning and the damage stretched for five kilometres (3.1 miles), with the eye of the storm measuring more than 10 metres (33 feet) across.

"Tornadoes in New Zealand are typically of that size, they're nothing like the size that are observed in the Midwest of the US," he told Radio New Zealand.

"So while it's a tragic and devastating event for the area it's passed over, in the broader scheme of things it's a relatively small tornado."

Another tornado struck Albany 20 years ago in May 1991, killing one man who was hit by debris while he was driving a bulldozer.