Arthur's Pass has been closed because of a massive slip and is expected to remain closed for two or three days.
The NZ Transport Agency's senior network manager Mark Pinner said a significant amount of rock and material was brought down on the highway by heavy rain over the past 24 hours.
The 100-metre-long slip happened about 1km west of Otira this morning, closing State Highway 73.
A second slip, about 20 metres long, happened further west at Aitkens, and flooding had been reported at Kelly's Creek.
Motorists were advised to take SH7 through Lewis Pass instead. Rail services have not been affected.
"As the rock and material are still falling onto the highway, our contractors are unable to get to the slip to begin clearing it," Pinner said.
"These things can be quite volatile."
Once the weather "receded", Pinner said contractors would be able to get up on the slip and "see what's been left hanging, as it were".
Given the volume of material that had slipped, he estimated it would take two to three days to clear.
SH6 through Haast Pass, from Haast to Makarora, also remained closed today after the heavy rain caused more rock and material to fall at Diana Falls.
Pinner said the slip "proves the need" for the work NZTA was doing to clear the Haast slips and put barriers in place.
It also reinforced the need for the overnight closures of Haast Pass that have been in place since late last year.
He said the new slips could hold up the clearance work, but in the long run it would be helpful to be more aware of the vulnerable land so NZTA knew what needed to be cleared and stabilised.
COAST WEATHER 'PRETTY NASTY'
Ngu Moses came across the slip this morning while attempting to drive home to Christchurch from Hokitika.
"It was definitely an impressive sight. It's a big slip. I've seen slips before near Kaikoura but this one was quite substantial."
The weather was "pretty nasty", with torrential rain and strong winds.
"We lost our wipers on our vehicle. A big gust of wind made them go one way, but too far one way."
Moses and his colleague, who had been on the West Coast for work, had to stop at a small service station near Reefton to get the wipers fixed, and hoped to be able to get home via the Lewis Pass tonight.
It was still raining heavily on the West Coast at 3pm, he said.
"It's not easing off. I'd be expecting more [rocks] would come down."
The bad weather could have contributed to a truck crash on the West Coast this afternoon.
The driver suffered suffered a shoulder injury after their truck rolled on the Kumara-Inchbonnie Rd near Lake Brunner about 1.20pm.
A St John spokeswoman said the driver was taken to Greymouth Hospital with minor-to-moderate injuries.
Grey Main School had one class in Arthur's Pass on a school trip. They were due back in Greymouth this afternoon, but with the road closed would have to take the "long way" home via Lewis Pass.
The detour will be an extra 450km for the children who will spend an extra four-and-a-half hours on a bus, arriving home about 7pm instead of 2.30pm.
Acting principal Terrye Drake said the kids were "absolutely fine" except that they would be late home.
She did not recall a previous time when a school trip had been affected by the pass closing.
Arthur's Chalet manager Thomas Mitchell said the road closure would not affect the business too much because "people knew there was going to be bad weather" and had not planned to stay the weekend.
He said there had been a "couple of people parked up at the [Otira] viaduct" but they seemed to have turned around.
He was preparing for a quiet weekend with few people travelling through.
BOIL WATER NOTICE ISSUED
The Selwyn District Council has advised residents on the Arthur's Pass water supply to begin boiling their water.
No E.coli had been detected in the supply yet, but heavy rainfall had increased the turbidity of the water.
A council spokeswoman said the water treatment method might not be effective and the council could not guarantee the water was safe to drink.
Residents were advised to boil all water used for drinking, brushing teeth or food preparation.
The boil water noticed was likely to be in place for several days.
MetService meteorologist Peter Little said rainfall on the West Coast had not been too heavy, with 65mm recorded in the past 24 hours at Haast. But he said in the hour between 9 and 10am this morning, there had been 13mm of rain in a Haast rain gauge.
"We normally consider 6mm per hour to be severely heavy rain," he said.
He said rainfall would have been higher in the mountain ranges.
Rain was already starting to ease around Fiordland, and would continue to clear as the front moved northward.
However heavy rain was expected to remain in the ranges of northern Westland, Buller and western Nelson into Saturday afternoon.
With 100 to 200mm of rain forecast for those areas, the MetService advised that rivers and streams were likely to rise rapidly and that further slips and surface flooding were possible.
MetService has issued snow warnings for some South Island roads. Snow showers are expected about higher parts of Milford Rd from late tomorrow afternoon, with three to six centimetres expected to accumulate between 4pm and midnight Saturday.
There is also potential for substantial snowfalls on Sunday, with 20 to 30cm possible.
A few snow showers are also expected on the Lindis Pass, above 800 metres. Up to 2cm could accumulate late Saturday afternoon.
- The Press
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