Police said there were "a handful" of weather-related incidents reported in the region. However, no one was injured.
Franz Josef and Haast have become isolated due to the State Highway being blocked on either side.
Haast Primary School and one other school have been closed today as a result, RNZ reported, and there is minor flooding between Hokitika and Fox Glacier.
Westland district mayor Bruce Smith told TVNZ's Breakfast show that 10 people had been evacuated in Haast overnight.
West Coast Group civil defence controller Te Aroha Cook told RNZ significant planning was underway, especially for the Buller District as more heavy rain was expected.
Authorities are concerned the Buller River could burst its banks again like it did last July.
The heaviest rain was expected from this afternoon through until tomorrow morning and then Saturday morning.
Those who can self-evacuate voluntarily are being encouraged to. About 22,000 sand bags were distributed around Westport yesterday to try and protect properties.
Local state of emergency
A local state of emergency for the Buller District has been declared as West Coast residents batten down the hatches and prepare to evacuate as torrential rain begins to hammer the region.
MetService has declared a red warning for Westland and Buller - with the potential for hundreds of millimetres to drop over 48 hours.
A large-scale response is kicking into gear, with West Coast Emergency Management setting up centres in Greymouth, Hokitika and Westport.
The NZTA is warning motorists in the whole of the South Island to be careful.
"Roads will be affected and driving will be treacherous in such heavy downpours. People may face delays."
A large-scale response is kicking into gear, with West Coast Emergency Management setting up centres in Greymouth, Hokitika and Westport. Photo / George Heard
Westland and wider West Coast
River levels throughout Westland and the wider West Coast are set to rise as rain continues.
Westland District Emergency Operations Centre (EOC) controller Simon Bastion said residents in the area should be prepared to evacuate their homes if needed.
"We are monitoring the situation closely and our local controllers are setting up community welfare centres to look after people if evacuations are called for. If you live in an area where flooding is a regular occurrence, we urge you to evacuate to friends and family as a first priority."
Community Response Centres are currently open in Franz Josef at the Medical Centre and in Harihari at the Harihari Community Hall.
Westport civil defence controller Bob Nixon said the rain was starting to pour down intensively at about noon yesterday.
He said they're encouraging people to voluntarily evacuate from low-lying sites in the town.
For people who live in areas that don't usually flood, Bastion said residents should have a "grab-bag" that holds what the person, family and pets need, including important documents.
Residents are reminded to take their emergency getaway bag with them and to remember medicines, food, water, a radio, torch, warm clothes and blankets.
Westland Mayor Bruce Smith said he anticipated flooding, road outages and possibly worse.
The Omoeroa River between Franz Josef and Fox Glacier this morning. Photo / Supplied
"We're just trying to get the message out to people to ensure that they fill their car up tonight - make sure it's full of petrol, ensure their standby plant has got fuel and that they've got basic groceries for two or three days, you know, it's basic Civil Defence stuff."
Warm winds and snow melt combined with a massive rain event and dry ground conditions meant it had the potential to cause quite a problem on the coast, particularly around Fox and Franz Josef glaciers, Smith said.
"I think there's a high chance there's going to be a number of unexpected slips and we don't want people getting trapped in between slips or, you know, getting caught in them unnecessarily."
SH6 closed between Makarora, Otago, and Fox Glacier, West Coast.
Waka Kotahi NZ Transport Agency said heavy rainfall in South Westland has closed SH6 early this evening between Makarora and Fox Glacier. The situation will be reviewed at midday today.
Elsewhere on SH6, there was surface flooding on low-lying areas of highway and motorists are advised to avoid travel in these areas if possible.
Hokitika and Greymouth
For residents in the Hokitika town centre, sandbags are still available to protect homes and businesses.
Meanwhile, in Greymouth four trucks and one support vehicle from New Zealand Army arrived in Greymouth. A Royal New Zealand Air Force NH90 helicopter will also fly south to be ready to assist with the response.
Preparations under way in Hokitika as heavy rain is set to hit the area. Photo / George Heard
An emergency operations centre had been stood up at the council building in Hokitika and Smith said he hoped people would stay off the roads unless travel was absolutely essential.
Buller District
A local state of emergency for the Buller District has been declared.
Mayor Jamie Cliene yesterday made the Buller District declaration, which allows Civil Defence controllers to direct and co-ordinate personnel, material and other resources made available and provides access to extraordinary powers to deliver an effective and timely response to an emergency.
The current weather event has the potential to cause serious flooding to parts of the Buller District.
Four trucks and one support vehicle from New Zealand Army arrived in Greymouth. Photo / NZ Army
"Members of the public are reminded to prepare getaway bags in preparation for potential evacuations tomorrow," the council said.
"If anyone is feeling unsafe, please self-evacuate to friends or family on higher ground."
The majority of residents at O'Conor Rest Home have been evacuated today to alternative accommodation
West Coast DHB Incident Controller Philip Wheble said some residents still at O'Conor Rest Home will be evacuated.
Cleine told the ODT the escalation of the rain warning heightened the importance of the region being prepared, and said planning was well underway for what could be a significant event for the West Coast.
The heavy rain was due to coincide with high tides and there was concern for those in the north of the Buller district in places like Mohikinui, Seddonville and Karamea.
A similar storm system caused significant flooding and high river levels in Buller and Marlborough mid last year. Photo / George Heard
All the ingredients were there for the weather event to be similar to the deluge that caused widespread flooding last July, with almost half of Westport's residents evacuated from their homes, and at least 100 homes rendered unliveable by the floodwaters, Cleine said.
Cleine said they were planning for the worst.
"What we learnt from July was that some of our traditional evacuation centres are sort of less than ideal in a town flooding scenario so a lot of work going in yesterday outside of town, effectively up on the terraces which obviously presents some logistical problem around where people can shelter."
