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Further tornadoes could strike in the next 24 hours, WeatherWatch warns, after a twister touched down in west Auckland this afternoon.
Powerlines were down and on fire, a house was struck by lightning and at least 13 properties were damaged when the tornado ripped through Avondale and Te Atatu South at about 1pm.
The Fire Service now estimates its path was about 1km wide.
Most of the affected houses sustained roof damage, others had fences and trees down and windows smashed.
A Fire Service incident control unit has been established at the intersection of Ash St and Wairau Ave, Avondale - the roads thought to have been worst affected.
WeatherWatch analyst Richard Green the tornado was "relatively minor" compared to May's twister in Albany, which killed 37-year-old Benedict Dacayan.
Most of the damage, too, seemed minor, he said.
"Fortunately it was short lived because if it had been a longer electrical storm, who knows what chaos could have resulted."
Thunderstorms had been forecast for the city this afternoon but not tornadoes.
"The system that was being looked at just revved up a little more as it passed over Auckland, which produced the tornado.
"It was basically just very warm air and cold air mixing."
Mr Green said another "disturbance" was approaching New Zealand from the Tasman Sea, which meant there was a risk of further tornadoes in western areas of the North Island for the next 24 hours.
Earlier in the day the wild weather ripped boats from their moorings, damaged powerlines and caused havoc for an Auckland yacht race, while MetService warned parts of the South Island could be in for a blizzard.
A massive gust of wind tore through the endurance race near the finishing line in the Rangitoto Channel at about 1.30am.
Auckland coast guard duty officer Katherine Andrews said it ripped the masts off two yachts and caused another to run aground.
"The wind just picked up like you wouldn't believe," she said.
Fire Service Northern Communications shift manager Jaron Phillips said a 10 metre launch was also pulled from its moorings in Kawakawa Bay, southeast of Auckland, at about, 7.45am.
Around the same time in Mills Bay, Northland, a yacht came adrift and had to be towed back to its mooring by a Fire Service rescue boat.
Power was cut for part of Waiheke Island this morning after high winds hurled a flag pole onto powerlines in Oneroa .
Sparks flew and power was down for parts of the island until the pole was removed, Mr Phillips said.
A family on Auckland's North Shore were woken by a loud bang after the powerful wind tore off part of their roof.
Firefighters nailed the one metre piece of roofing iron back on to keep the weather out, Steve Sosich of East Coast Bays Fire Station said.
MetService has issued severe weather warnings for Southland, Otago, Wairarapa and Hawke's Bay and said gale force winds could spread over much of the North Island tomorrow.
Snow is expected to low levels over the deep south tomorrow, with the possibility of heavy falls above 300 metres.
Winds are also expected to reach gale-force for coastal parts of Southland and Otago on Monday and Tuesday, creating potential blizzard conditions near the coastal hills.
MetService advised farmers in affected areas to move vulnerable stock to sheltered locations.
Forecaster Stephen Glassey said Northland and Auckland could be in for thunderstorms this afternoon and evening.