Live: Tornados strike coastal town - 41 warnings as wild storm batters NZ

Massive snowfall in Glenorchy. Video / George Heard

At least two small tornados have caused damage on the Kapiti Coast, north of Wellington, tonight as great swathes of New Zealand batten down the hatches to guard against a rolling line of thunderstorms striking the country.

There have already been 21,500 lightning strikes over land and water in 12 hours, MetService says, with more thunderstorms on their way.

And as of 5pm, there were 41 warnings and watches across the country - including 18 across the North Island and 23 on the Mainland - as forecasters warn of a stormy night ahead.

Severe thunderstorm warnings have been issued by MetService for Wellington city, Porirua, Hutt City, Upper Hutt, Kapiti Coast, South Wairarapa, Taranaki and up the West Coast beyond Raglan, and extending south across a choppy Cook Strait to Marlborough, Nelson, Buller and the Canterbury high country.

Small tornadoes have also reportedly gone through Waikanae Beach, Kapiti Coast, this afternoon and early evening.

Reports on social media suggest windows and doors have been blown in, with uprooted trees and damaged cars.

One local wrote on social media that their trampoline was now gone and that the experience was 'f*****' scary".

The first tornado was spotted around 4pm – while another was reported to emergency services just after 7pm.

MetService duty forecaster Gerard Bellam said heavy rainfall in the area – with 20mm an hour between 4pm and 6pm, and another 16mm between 6pm and 7pm – could produce that sort of weather activity.

"There is a line of active thunderstorms crossing that area at the moment," he said.

MetService earlier warned that small tornadoes could come with the severe thunderstorms rolling across the country.

Waka Kotahi NZTA also warned of strong winds on the Auckland Harbour Bridge and told motorists to prepare for its possible closure.

MetService was forecasting wind gusts of between 80 and 100km/h from 8pm and through to tomorrow night.

High-sided vehicles and motorcyclists were advised to use SH16 and SH18 as an alternate route.

Earlier, MetService's weather radar detected the line of severe thunderstorms moving towards the southeast.

Forecasters expect them to be accompanied by torrential rain, large hail, damaging wind gusts, and even small tornadoes.

Flooding has already closed roads and threatened properties around Porirua today and locals and motorists are being warned to watch out for surface and/or flash flooding about streams, gullies and urban areas, and hazardous driving conditions.

Heavy rain kept emergency services busy around Porirua, with firefighters attending seven to eight callouts since midday, where water was threatening people's houses.

Fenz central shift manager Karen McDonald said the water had not managed to get inside most houses but was threatening to.

It comes as wild winter weather swept across the country today.

It's still snowing in the lower South Island, though not at altitudes as low as Saturday when snow was down to sea level, but it's still blocking roads in some areas.

Snow blanketed parts of Central Otago yesterday, bringing joy to the region's ski fields, with Cardrona ski field opening early and other southern mountains set to follow suit in the coming days.

Road snowfall warnings have been issued for the Desert Rd, Lewis Pass, Arthur's Pass, Lindis Pass, the Crown Range Rd and Milford Rd.

Waka Kotahi NZ Transport Agency said Lindis Pass was closed just after 10am because of heavy snow, while snow had also closed Milford Rd and the Crown Range Rd.

MetService meteorologist Stephen Glassey said for Auckland, Northland and Waikato the main thunderstorm risk would be overnight.

"It's very stormy weather across many parts of the country ... as well as squally thundery showers, there's also strong winds and heavy rain," he said.

The weather system was sitting in the Tasman Sea but had come up from the south and had brought a lot of cold air with it. Eastern areas that were more sheltered were not getting such bad weather, Glassey said.