Up to eight vehicles are trapped in the lower Buller Gorge after heavy rain caused two slips.
Police said eight vehicles are currently trapped between the two slips on State Highway 6, between Inangahua Junction and Westport.
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The trapped people were safe and unharmed, a spokesman said.
The slips were caused by heavy rain late this afternoon.
A NZ Transport Agency spokesman said the exact number of vehicles trapped could be lower, and contractors were working from both sides to get the trapped people out as quickly as possible.
Meanwhile, residents did not have to evacuate low-lying areas along the Rakaia River after water levels peaked following wild weather.
Earlier today, a police spokesman said the Rakaia River was extremely dangerous as water levels were rising very quickly with water almost across the road on the northern side of the Rakaia Gorge Bridge.
Rakaia Huts resident Clarke Wilkes said the river peaked at 5246 cubic metres per second (cumecs) at 4.45pm. The water level was normally at about 1500 cumecs.
Wilkes said people had been discouraged from going to the river mouth on motorbikes and the main boat ramp had been cordoned off yesterday evening, but no one had needed to evacuate the village.
Today up to 1000 West Coast homes lost phone and internet access - including emergency calls.
A key fibre cable servicing areas south of Harihari was knocked out when a one-lane bridge over the Wanganui River was washed away. State Highway 6, the only highway along the coast, was also cut off.
Snap chief executive Mark Petrie said the cable was used by nearly all telecommunications companies to provide services to the area, with about 1000 homes south of Harihari believed to be affected.
"They're completely isolated down there: they've lost phone, internet and mobile."
Petrie said the outage would also prevent residents from making emergency calls to 111.
Satellite phones could be used as a temporary fix, while a technician was likely to be monitoring the phone exchange for emergency calls.
Petrie said Chorus, which owns the cable, had estimated that access could be restored by 10.30pm tonight.
Police said the road would be closed for some time, with the only detour a lengthy one back to Wanaka for anyone wishing to travel north from areas such as Haast, Fox and Franz Josef Glaciers.
"They can't do anything [about the bridge] until the weather subsides, because it's pretty rough over there," a police spokesman said.
State Highway 73 - the West Coast's main roading link to Canterbury - was also closed from Arthur's Pass through the Otira Gorge to Jackson's, with flooding on parts of the road and high winds causing several trees to fall over and block some areas. The alternative roading link between the regions is via the Lewis Pass on State highway 7.
WORST TO COME
A front covering the area was bringing heavy rain and thunderstorms, and was expected to move onto the lower North Island later today.
A representative from the Department of Conservation visitors' centre in Arthur's Pass National Park said the centre had not received any reports of issues with trampers in the area.
While the tracks had not been closed, trampers were being advised not to use them because of the many river crossings in the park.
Earlier the weather had trapped more than 100 trampers on the Milford Track but the track reopened this morning.
A spokesman from Metservice said the system was moving over the area rapidly, with the worst weather expected overnight.
"As it goes past it's going to bring a burst of heavy rain to Buller and North-West Nelson, and the Tararua Range," he said.
"There's a full warning out for Buller and north-west Nelson - 180-200mm of rain could fall there between now and midnight."
He said the weather will deteriorate throughout the day as the front comes closer.
Wind is also picking up in the lower North Island, with northwesterlies reaching gale force.
Wellington and Wairarapa, Marlborough and south of Masterton could see winds of 120 kmh to 140 kmh.
"Wellington will probably have to wait until this afternoon or this evening before the rain sets in, but it's already starting to settle onto the top of the South Island, at least in the west," he said.
"Certainly the conditions for rain and wind are going to deteriorate throughout the day today."
Wind warnings are also in place for Taranaki, Taihape, Wanganui and Manawatu.
Metservice said winds of this strength have the potential to damage trees and powerlines, and make driving difficult.
Westland and the Southern Alps could see 500mm to 600mm of rain in some places, with significant spillover into Canterbury.
Heavy rain and wind warnings for Fiordland and Otago have been dropped.
- © Fairfax NZ News