Fierce front batters New Zealand

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Lightning strikes have started large fires and strong winds have toppled trees, powerlines and torn roofs off houses in Canterbury as a storm batters the lower part of the country tonight.

Emergency services were fielding hundreds of calls from the region with nearly all Fire Service appliances required to meet the heavy demand, said spokesman Jaron Phillips.

"There is a lot of damage to properties, roofs off buildings, trees down, tiles lifting," he said.

Of particular concern was a large fire in a private forestry block on Cramptons Bush Rd, Hurinui, he said.

A fire with a front of about 500m was "ripping across the top of trees" and fallen debris was preventing eight appliances from entering the area.

There were other large fires around the district, too. In West Melton a hedge fire had spread to a shed, in Ashburton a burning cluster of trees threatened housing, and in Leeston there was a fire at the local showgrounds.

Emergency services in Wellington also reported a small amount of damaged to roofs and signs.

St John reported no injuries from the events that included trees falling on occupied cars.

The lower south Island has been battered by a fierce front that has wreaked havoc and forecasters warn it is on its way north.

MetService has issued severe weather warnings for the lower half of the country as the front moves over the South Island before moving over the lower North Island tomorrow.

Fiordland bore the brunt of the front this morning with heavy rain and a spectacular thunderstorm which heralded the arrival of the bad weather.

Cromwell resident Jade McLellan said what she thought was a tornado picked up her father's 9-metre boat off a trailer and flung the two-tonne vessel over the neighbour's fence about 11am.

"We had a big gust of wind come through which picked up the neighbour's trampoline and spun that above fence level. Then we saw the boat flip up off its trailer and into the next door neighbour's yard. Now it's quite demolished," she said.

Neighbours had seen what they thought was the funnel shape of a tornado approaching their house about 11am.

"The wind really picked up and was throwing itself on the house and mum was yelling at everyone to get into the lounge. As I came through the hallway I looked through the sliding door and saw the boat flipping. It's quite crazy," Ms McLellan said.

Fire Service southern region operations manager Chris Munro said the South Island's firefighters had been very busy with weather-related calls today.

"We've got multiple calls at the moment: trees down, powerlines down, grass fires caused by the powerlines, trees down across the road."

Firefighters were also called when a house in Fox Glacier township caught fire after being struck by lightning around midday.

It was out by the time crews arrived, Mr Munro said.

The majority of calls were from Otago and Canterbury but there were also some small jobs on the West Coast due to heavy rain.

Dunedin police said motorists travelling between Oamaru and Dunedin should take extreme care as severe winds battered Otago's east coast.

They were attending two traffic incidents on State Highway 1, including a truck which overturned due to heavy winds.

The driver received minor injuries.

Air New Zealand said a number of flights to and from Queensland and Dunedin had been diverted or cancelled.

Affected passengers were being accommodated on other air services or by road, the airline said.

MetService said the front was expected to reach the lower North Island tomorrow night and clear the upper North Island overnight Thursday.

A brief burst of heavy rain was also expected to affect the Tararua Range, Mount Taranaki and the North Island central high country late tomorrow and early Thursday.

"This is a significant amount of rain and people in the affected areas are advised that rivers are likely to rise rapidly with the risk of flash flooding," the MetService warned.

Northwesterlies were expected to reach severe gale-force for most eastern parts of the South Island and Fiordland, as well as in Wellington and the east of the North Island.

Gusts could reach 140km/h in parts.

"Winds of this strength are likely to bring down trees and powerlines, and make driving dangerous, especially for motorcycles and high sided vehicles."