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Thousands of homes remain without power and rail lines north of Dunedin are closed as the storm which battered the South yesterday moves north.
Some Canterbury residents can expect to be without power for up to five days.
Lines company Orion's Chief executive Rob Jamieson said power was out to 17,000 Orion customers this morning, down from 28,000 overnight when strong winds affected power lines across the network.
Most power cuts were due to trees or branches falling onto power lines.
Power had been restored to most of urban Christchurch, and affected areas were predominantly in the rural region west of the city, Mr Jamieson said.
Half of Orion's major rural substations were without power and teams were continuing to assess the extent of the damage, he said.
"Until we are able to bring the substations back on line, it is difficult to determine the extent of the damage throughout the rest of our rural network.
A severe weather watch is in place for Waitomo, Waikato, Marlborough and Nelson.
A burst of heavy rain in Waikato and Waitomo was expected tomorrow, senior forecaster Erick Brenstrum said.
"An active front should move slowly north over the South Island to lie across Cook Strait at midnight tonight.
"It should then cross the North Island on Thursday. This front is preceded by a very strong northwest flow and there are warnings for severe gales for many areas."
Northwest gales could reach severe gale force in Nelson and inland parts of Marlborough today, Mr Brenstrum said.
Over Westland, widespread severe gales were no longer expected, but a watch was in place for severe thunderstorms which may produce wind gusts exceeding 120km/h over localised areas.
"People in these areas are advised to stay up to date with the latest forecasts."
A KiwiRail spokeswoman said rail lines were closed between Blenheim and Dunedin, and between Haast and Rolleston due to extremely high winds which brought trees down over the tracks overnight.
"We've also got a number of level crossings out of action but there's no trains running on them.
"We've had staff on-site since first light making repairs. We expect an update later this morning."
In Wellington, a tree which fell over the tracks on the Wairarapa line this morning caused a 20 minute delay, but the service has since resumed, the spokeswoman said.
Power out in Canterbury
Canterbury residents have woken up this morning to downed trees, power cuts, roofs damaged and tiles lifted, the Fire Service says.
Since yesterday afternoon, the service has answered more than 1000 calls from locals reporting damage to their properties from savage winds that tore through the area.
Those gusts were now heading up the country and will hit the capital about midday.
About 19,000 Canterbury customers remain without power and lines company Orion said while the wind was still strong, there was no time frame on when power will be reconnected.
Orion's chief executive Rob Jamieson said at the storm's worst, 28,000 customers were without power overnight.
Fires ignited in rural areas overnight.
A large blaze burnt about 200ha of forest at Ashley Forest, west of Amberley, southern fire communications shift manager Brent Dun said. The blaze was now contained.
Another large fire at a plantation west of Kaikoura was ignited by a downed powerline, Mr Dun said.
"Rural fire are in attendance there and are on top of things."
Numerous other vegetation fires overnight had been extinguished.
"They've been caused by power lines being knocked down, lightning strikes and previous controlled burns which have just been whipped up by the winds," Mr Dun said.
"Really today it's about mopping up and seeing to the public - seeing if they're okay and helping out with damaged houses."
The wild weather has caused disruptions to air traffic, with flights to and from Christchurch and Wellington affected.
A Christchurch Airport spokeswoman said the airport was closed for a couple of hours overnight but reopened at 1.30am today. Flights were operating as normal this morning.
In the capital, the airport remains open this morning but some flights to and from Wellington Airport have been diverted or cancelled due to high winds.
An airport spokeswoman said passengers should check whether their flight has been affected, either on the airport or their airline's website.
Flights to and from Auckland Airport were unaffected, other than those disrupted due to the weather at other centres.
MetService meteorologist Daniel Corbett said the weather front was a "dogs dinner, and it's not done yet".
Norwesterlies from the active front over central parts of the South Island brought wind gusts up to around 130km/h at Christchurch Airport last night, Mr Corbett said.
"Some of the surrounding hills got gusts up over 150km/h."
The storm also brought heavy rain and thunderstorms, Mr Corbett said.
In the last two hours there had been more than 3000 lightning strikes in the front across all of New Zealand.
"Most of them have been centred off the South Island. It is just lit up like a Christmas tree."
The rain had been "piling in", he said.
In the past 24 hours Arthurs Pass had seen 265mm of rain and Mount Cook village had 247mm of rain fall.
The front was moving north with all of its rain into northern Westland and Buller, Mr Corbett said.
"We still have loads of warnings for the rain and of course the wind which is still strong through Cook Strait for much of the day, and then the wind's focus will shift more towards Hawke's Bay [and] Gisborne."