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LATEST: Three people are dead and seven injured after a tornado ripped through the Auckland suburb of Hobsonville, with police ordering people to shelter in their homes amid fears of further twisters.
All flights from Christchurch to Auckland are delayed.
An Auckland Airport spokeswoman said operations have resumed at the airport, however there are significant delays to domestic and some international flights.
Passengers should consult the arrivals and departures information on the Air New Zealand website for schedule information, she said.
Former Cantabrian Jazz Thornton, who moved to Auckland this year, said there was "heavy rain and thunder".
"My best friend who I live with said the house was rumbling and the rain was so heavy. She thought it was going to smash the windows."
Her friend's mother, Katherine Hemmingway, was in West Auckland when the tornado hit.
"I was on the motorway and suddenly couldn't see, everyone had their lights on and windscreen wipers going but it was white outside," she said.
"So scary. Most of us pulled over to the hard shoulder as soon as we could and waited until we could see again."
Canterbury journalist Emily Cooper, 24, is in Auckland for work and said the storm was "very scary".
"The weather was so bad. All of a sudden it just got really windy and began pouring down. It was actually quite frightening."
She was stuck at Auckland Airport, unable to get a flight back to Christchurch.
As she was speaking to The Press, it was announced lightning had struck the runway.
"I really don't want to get in a plane on this. There are massive delays all over."
Former Christchurch woman Laura Weaser was in Auckland's CBD when the wild weather hit.
"There was a lot of thunder and torrential rain. It became dark very quickly and also there was a noticeable drop in temperature."
She said there was terrible flooding in surrounding suburbs.
A University of Canterbury weather expert described Auckland's fatal tornado as a "furious image on the radar".
Meteorology lecturer Marwan Katurji said a forecast of damaging winds and severe hail was put in place before the storm.
"It might've been gale winds from the severe thunderstorm or a microburst - strong winds converging at the surface from above,'' Katurji said.
Katjuri said the Auckland region was one of "the hot spots" which promoted tornados.
''In Canterbury we are blessed with the Southern Alps that do shield off the severe westerly storms. But occasionally we do get the odd small waterspout off the Banks Peninsula coast.''
The tornado, which hit about 12.15pm, ripped roofs from houses, toppled trees and sent debris flying on to cars.
Hobsonville Point residents have been ordered to take shelter in their homes and cars with the MetService warning of the potential for further tornadoes.
Police have set up an operational base at the worst-hit Whenuapai.
Urban Search and Rescue were in the area at the time on a training run and have been called in to help check houses.
But it is understood several downed power lines in the area are preventing search teams from getting to some buildings.
Toni Hayward, administrator at the Open Wananga Office in Hobsonville, saw the tornado rip through.
"It came right through here and picked stuff up an threw it on the road."
"The sky went all dark and there was a big clap of thunder, all the trees were flattened."
There are now severe thunderstorm warnings for the Waikato area.
Ambulance staff reported two deaths from the storm at a construction site in West Auckland. A third death was later confirmed.
There are reports of multiple injuries across the northwestern suburbs. A construction worker on a new high school site at Hobsonville told Radio New Zealand there were people missing and many people injured.
"Pretty bad," a man, quoted only as Sam, said.
"We did a head count, I think there are a couple of people missing."
An ambulance spokeswoman said five crews were attending different scenes.
"We are currently assessing seven patients all in and around Hobsonville."
Twenty fire trucks are dealing with 80 properties mainly in Hobsonville and surrounding west Auckland suburbs.
Roofs being blown off and flooding are the main problems being dealt with, fire communications shift manager Peter Stevenson said.
Earlier reports indicated people were trapped but they have since been rescued. However, there were potentially others trapped, Stevenson said.
North Shore Hospital’s emergency department is assessing four patients with tornado injuries, though their status or the type of injury is not yet known.
Patients are being sent to North Shore because it has a larger emergency department than Waitakere.
Waitakere Hospital has suffered surface flooding in an outpatient area.
No one has been evacuated and the hospital is functioning as normal, communications spokeswoman Ashley Campbell said.
Power is out at the Hobsonville shopping area.
The New Zealand Transport Agency said State Highway 18, the upper harbour motorway, was closed between Brigham Creek Rd and Greenhithe Rd due to debris on the road.
Hobsonville RSA cook Deborah Carlson said she was trapped in her car during the storm, too terrified to go outside.
"I was just sitting there because it was pouring with rain and I thought I'd wait it out. But then my car starting shaking and there were things flying everywhere. I thought it was going to flip, I was terrified."
Carlson said she didn't know what to do, so called her boyfriend.
"I was in there by myself for about 15 minutes. The bins were flying past and the gates were swinging open, it was horrible."
She said when she finally left the car, the scene was a mess: "There's debris everywhere."
Casey Davenport, who lives in Hobsonville, was at work when the weather started to turn.
"Then it just came down, and it looked like mini tornadoes - the rain was just like being swished around a lot."
"Then somebody gave me a call and said that somebody's house from work had been taken out and I was like 'oh God'. Not fun."
Fallen or uprooted trees and pieces of debris were blocking the road to her house, which she said now is "leaking like a sieve".
"We're missing tiles, broken windows ... it's full of water now because it's leaking. But we're one of the better ones I think."
Brendan Muir, who is working at Hobsonville Point, said he was sitting in a ute when the tornado hit.
"It was just mayhem. I had to put my seat belt on, I thought it was going to flip."
Muir said that, around him, he could see trees "that looked like a plane had crashed into them", walls and fences knocked down and Portaloos scattered about.
He said for about 10 minutes there were so many sirens sounding it "seemed like 9/11".
Despite threats of another tornado on the way, Muir said he was back pouring concrete.
The storm has destroyed houses in the air force's married quarters in Clark Rd, Hobsonville.
A witness said the roof had been ripped form at least one house, and a tree had smashed through the kitchen of a house nearby.
Trees have been uprooted, a trampoline flipped and fences crushed by the force.
Frances Schuster said the tornado only lasted 12 seconds but was terrifying.
"It went blurry for a while, it just happened so fast. It was really loud and the windows were shaking."
Part of a roof fell on to her car.
PM, MAYOR RESPOND
A spokeswoman for Prime Minister John Key - the MP for Helensville, which includes Hobsonville - said he is being kept informed of the situation.
"Emergency services are currently responding. People are being advised to remain indoors and to avoid the area, if possible."
She added: "The Prime Minister will continue to assess the situation as information becomes available throughout the day."
Auckland Mayor Len Brown says he was very concerned at casualties on Hobsonville Point.
"Also reports of surface flooding and damage in other parts of Auckland. Please stay safe and if possible stay inside until the weather clears," he said on his Facebook page.
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