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Southlanders are being asked to stay at home and travel on roads only if it is absolutely necessary.
Around 10cm of snow has fallen across coastal parts of Southland, making roads particularly dangerous.
Police are concerned with the number of drivers out on the roads, considering how hazardous they are.
A number of cars have slid off the road in Invercargill, causing minor damage with no injuries.
Emergency Management Southland says all roads are open but some are marginal.
Spokesman Neil Cruickshank said there was potential for further snow showers and ice overnight.
He said there was also a possibility of power outages in some areas.
A heavy rain warning remains in place for Fiordland, the ranges of Westland south of Otira, and the headwaters of Canterbury and Otago rivers.
A severe weather warning remains in place, and the MetService advises that another fast moving front is expected to cross the South Island today and will move onto the North Island this evening.
A heavy snow warning was added for Southland and South Otago today.
High winds and rain created havoc around the country overnight, felling power lines and cutting electricity to tens of thousands, including dairy farmers desperate to milk their cows.
SH1 north of Bulls is closed because of flooding and detours are in place while slips and surface flooding have closed SH3 at Ratana.
A 100m stretch of SH1 was covered in water up to 1.5m deep where it went under the railway overbridge near Marton, forcing a local detour, said Inspector Ken Climo of police central communications.
One car had driven into the water and had to be rescued, he said.
"There are problems all over the place. State Highway 3 is closed in two or three places."
There were also slips on SH4 and the Manawatu Gorge had been closed at various stages this morning while power lines had come down is some places, he said.
"There's been quite a weather bomb go through there, and it's caused havoc."
However, the volume of calls had dropped since the morning, which indicated the problems were abating, he said.
According to Radio New Zealand, the Manawatu-Whanganui Regional Council says it has closed the floodgates on the Makino stream to protect Feilding from flooding.
Meanwhile, the NZ Transport Agency said SH1 between Woodlands and Edendale in Southland had reopened following heavy snowfalls.
Southland Area Engineer Peter Robinson said contractors have been working to remove the snow with ploughs and were applying grit to the road.
However, snow was still falling and people should only travel if it was absolutely necessary, he said.
State Highway 94 Te Anau to Milford Sound and SH87 Outram to Middlemarch have both been closed because of heavy snow and the Chaslands Highway, through the Catlins, will be closed from 5pm tonight.
Storm cuts power to thousands
Lines company Powerco said this afternoon it had restored supply to around 28,000 customers as a severe storm continued to pound the North Island.
Network operations manager Phil Marsh said the storm had caused power cuts to around 45,000 customers through the middle of the North Island in the past 24 hours.
Gale force winds and lightning caused a large number of power cuts with trees being blown into overhead lines and snapping power poles as well as lightning strikes damaging transformers and related equipment.
"There are currently around 17,000 customers without supply with the worst affected areas being Thames, Coromandel, Kerepehi, Paeroa, Te Puke, Whanganui and Kimbolton," Mr Marsh said.
People should keep well away from downed overhead lines and any other damaged network equipment, he said.
Fonterra warned farmers its trucks could not return to the Edendale milk factory today.
Mr Marsh said Powerco had received a number of calls from dairy farmers needing urgent restoration of power supply in order to milk cows.
"We have around 100 field staff working to get power back on to customers as soon as possible, but the conditions are challenging and in some areas we have multiple poles to replace and lines to untangle from fallen trees before we can reconnect supply."
Mr Marsh said repairs crews had been hampered by lack of access to some areas due to trees falling across roads.
"We are making good progress with repairs today. However the bad weather continues to cause damage, more recently around Wanganui, and it is clear some of the affected customers will be without power tonight."
Overnight, winds reached hurricane force at Manukau Heads, a farming community west of Auckland Airport, WeatherWatch.co.nz head weather analyst Philip Duncan said.
Gusts peaked at 154km/h, and felled power lines, cutting electricity in Warkworth, Remuera, Mangere and large parts of west Auckland.
Electricity lines company Vector believes about 30,000 people around Auckland lost power at some stage during the storm.
Around 2000 people in the Auckland area were still without power this morning, of which about half were in Piha, west of the city.
Vector told Radio New Zealand it hopes to have supply restored by means of a generator to 1000 customers there by 5pm.
Weather advice: Stay indoors
People planning to visit west coast beaches in the Auckland region were advised to check weather warnings before venturing out this weekend.
A heavy rain warning has been issued for the Central North Island and up to 100mm is expected in the Tongariro National Park.
The MetService forecast a 6m swell off the North Island's west coast.
There were more than 100 lightning strikes in the Hutt Valley and Wairarapa region yesterday, setting fire to a shed and trees.
Snow was expected in the North Island's central high country today while thunderstorms and snow were also expected to continue in the South Island, with particularly heavy snowfalls south of Mt Cook.
Northwesterlies should strengthen over central New Zealand as this front approaches with severe northwest gales returning to parts of Hawke's Bay, Wairarapa, Wellington and Marlborough.
While severe wind warnings are being eased today the blustery westerly flow is likely to remain for many North Islanders until the middle of next week.
- NZPA