A state of emergency has been declared in the Westland District Council Area which ranges from Hokitika South, to Haast.
Civil Defence is responding to heavy rain across the South Island.
West Coast Regional Council has activated its Emergency Coordination Centre (ECC) due to the conditions.
"[The ECC] has been activated with a full staff presence to monitor the large weather system," Civil Defence said in a statement.
The ECC will organise the region's response to the severe weather.
It is expected to remain open until Thursday evening. All rivers across the district are running high, and many have reached "alarm levels" according to the ECC.
The Waiho Bridge, south of the Franz Josef township has been destroyed by the surging waters.
Residents who live south of the Arawhata Bridge are self-evacuating.
"We are continuing to monitor [the rivers] and will ensure preparations for emergency actions," said Public Information Officer, Diane Maitland.
South Westland Area School has been closed, and river levels continue to rise.
Westland District Council reports the intensity of the storm is expected to increase throughout the day, and will dissipate early on Wednesday morning.
Metservice has updated its severe weather watches to include parts of the North Island as the front creeps across New Zealand.
Meanwhile, a section State Highway 6 has been shut down due to extensive rainfall.
The closure extends from Makaroroa to Hokitika.
All traffic between these two points will be stopped.
The highway was originally closed between Fox Glacier and Franz Joseph, but detriorating conditions have led to this stretch of road being extended.
Two slips have covered the highway, and the road will remain closed until Wednesday morning.
New Zealand Transport Agency says more slips are expected.
Two slips have covered the highway, and the road will remain closed until Wednesday morning.
New Zealand Transport Agency says more slips are expected.
"Given the rainfall intensity, we will keep this stretch of highway between the glaciers closed today as we are anticipating more slips and it is not safe for people to be on the highway in these conditions," said Transport Agency Network Manager Colin Hey in a statement.
Hey has advised motorists on other parts of State Highway 6 to avoid all non-essential travel.
Areas of the West Coast have been issued with heavy rain warnings as more than 370mm of rain fell overnight in Fiordland.
A slow-moving front is making its way across the West Coast, and Metservice meteorologist Georgina Griffiths told The AM Show it is expected to dump half a metre of rain on the western ranges.
"This is an exceptional rain event, the warnings have put half a metre of rain or more into the ranges of Westland."
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She said the rain will not only hit the ranges, but out near the coast in Milford, and over the ranges if wind persists.
"For the West Coast it's going to produce exceptional amounts of rainfall in the ranges but unusually also on the coast as we've seen with Milford sound, and a significant spill-over event for eastern parts of the divide."
"It's been 20 years since we've seen the rain levels that we're currently seeing at Milford sound, 430mm in the gauge already recorded there. "
Pictures captured by road crews show extensive flooding along Kinloch Road and Wanaka Mt Aspiring Road.
Griffiths says the wind is helping to push rain over the ranges to the east.
"That wind at the top of the height of the Southern Alps is important, if it's a really decent severe northwest gale, it will help the rain get up and over the divide."
Westland mayor Bruce Smith told The AM Show people need to make sure they're not putting themselves in danger.
"The message is clear; if you don't have to go on road into south Westland then don't, there is surface water from Franz through to Hari Hari, so keep off roads if you can," he said.
He said rivers in the area were expected to rise in the coming day.
The West Coast is no stranger to heavy rain, and Smith said he hoped the terrain would handle the downpour.
"We are going to get a lot of rain and we're certainly hoping we've got our finger on it."
Newshub.
