Storms lash North Island as voters head to polls in final hours of NZ's general election

Severe thunderstorms are hitting parts of the North Island on the final afternoon of New Zealand's general election, with flooding and storm damage already reported in Auckland.

A home in Wairau Valley had its roof collapse during the weather, while another house in Totara Vale was flooded.

Fire and Emergency New Zealand said it had received a couple of weather-related calls across Auckland by 5.30pm, including the roof collapse and flooding. One fire truck was sent to each incident.

The latest severe thunderstorm warning covers Auckland city, Waikato, Franklin, Rodney and Albany, with storms moving towards the southeast.

Another warning has been issued for Waikato, Waipā, Waitomo, Taupō, Ruapehu and Ōtorohanga, where thunderstorms are expected to bring torrential rain and large hail.

MetService meteorologist Devlin Linden says the storms have been building across the North Island and are expected to continue into the evening.

A billboard was brought down by strong winds in Grey Lynn, knocking over fencing and blocking part of the footpath, cycle lane and road. Photo/RNZ/Josie Campbell

"Quite a lot of activity along much of the western North Island, right the way from Auckland down to Taranaki and that western flank, but there is also a good amount of activity in other places around the country.

"These storms are convective storms and are driven by heat thoughout the day. It's expected they're likely to continue though to early this evening, when things start to cool down," Linden said.

Auckland was hit by heavy rain and hail during the afternoon, while strong winds brought down a billboard in Grey Lynn between Elgin and Northland streets.

MetService rain radar at 5pm Saturday. Photo/MetService

The billboard knocked over fencing and ended up across the footpath, cycle lane and road.

Lightning also delayed the Auckland FC and Wellington Phoenix derby at Go Media Stadium.

Further south, part of the roof outside the Cotton On store in Blenheim collapsed under the weight of rain. No one was injured and the store has since reopened.

The latest storms follow a busy night for emergency services across the country.

MetService recorded nearly 2000 lightning strikes across the top of the North Island overnight, while heavy rain in the Bay of Plenty reached 33.5mm an hour.

Fire and Emergency responded to five weather-related callouts overnight, including flooding and reports of fallen trees.

The wider severe thunderstorm watch stretches across large parts of the country, with a moderate risk of severe thunderstorms from Auckland and the Coromandel Peninsula in the north to inland parts of the South Island north of Tekapo.

The watch also includes the Bay of Plenty, central high country, Taranaki, Whanganui, northern and eastern parts of Wellington, Tararua and Wairarapa.

MetService says severe thunderstorms could bring localised downpours of 25 to 40mm an hour. Rainfall at that rate can cause surface and flash flooding, particularly around streams, rivers and narrow valleys, and can trigger slips.

Road users are also being warned to expect poor visibility and surface flooding during the heaviest rain.

With voting closing at 7pm, people who have not yet cast their ballots should check the latest weather warnings before travelling and take care on the roads.