UPDATE 6pm: A FREAK tornado struck Auckland today, killing one person and injuring dozens more as it ripped the roof off a suburban shopping centre.

Packing winds of 200km an hour, the twister hit the suburb of Albany without warning at about 3pm (12pm AEST), 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 centres 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 shopping centre, 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 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.

One witness told Sky News that cars were crushed with people inside.

A North Shore police spokesman said emergency services were fielding dozens of calls from the public, with reports of damage to homes and cars.

Martin Sibrits, of Rebel Sports, told Fairfax New Zealand the tornado was "simply unbelievable''.

"It was huge. I could see pieces of iron flying through the air, 100 metres up,'' he said.

He said the neighbouring Placemakers hardware store had taken the biggest hit.

"That place is looking like a bomb site.''

From his window he could see many cars in the parking lot had been damaged and several injured people were seeking help.

Ross Sims, of Mainline Music, told journalists he mistook the tornado for an aeroplane.

"I thought, 'geez that plane is low' but when I looked outside it was this giant big black cloud,'' he said.

New Zealand is hit by 20 tornado events each year, but they are typically very narrow and short-lived.

The worst of them hit the North Island city of Hamilton in 1948, killing three people, injuring 80 others and destroyed more the 200 homes and businesses.

New Zealand Metservice meteorologist Peter Kreft said the tornado hit without warning and the damage stretched for 5km, with the eye of the storm measuring more than 10m 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.

Originally published as Killer tornado rips through Auckland