Welfare centres are being set up in Greymouth as heavy rain floods homes and properties.
Grey District Council was warning locals severe weather was expected to start around 1pm and continue into the afternoon.
A deluge of rain was already causing surface flooding and residents were reporting sodden houses and backyards beginning to resemble lakes.
More than a dozen roads were closed.
A post on the Grey District Facebook page urged those with houses at risk of flooding to put their belongings up high.
"If you need to leave your property, people are welcome to go to the welfare centre set up at the Westland Recreation Centre, High St," it said.
Torrential rain caused chaos on State Highway 67 along the West Coast this morning, with the Transport Agency warning motorists of flooding and surface debris.
A heavy rain warning was in place for Westland and Buller, where heavy outbreaks of rain were expected to continue until early Friday morning.
While some considered the flooding good news following a long period of drought in the area, Weather Watch was calling the rain "too much of a good thing".
"Heavy rain yesterday, overnight and this morning has led to flooding in Greymouth on the West Coast with more rain coming."
According to MetService 120-160mm of rain could accumulate between Seddonville and Haast from Wednesday night to Friday morning.
Further east in Christchurch, stormwater grates are being checked and temporary pumps prepared as another onslaught of heavy rain approaches.
The weather forecast for today and leading into tomorrow suggests sustained downpours could cause surface flooding.
Christchurch City Council said a close watch was being kept on rainfall levels across Christchurch and Banks Peninsula.
"The forecast suggests Christchurch and Banks Peninsula can expect between 40 and 60mm of rain over the next couple of days," said city services general manager David Adamson.
"It is possible we will see some surface street flooding in some pockets of the city."
Council contractors were checking stormwater grates and sumps around the city to make sure they were free of debris that could block pipes.
Temporary pumps had also been sent to the Flockton area, Maces Rd and Ebbtide Rd in case of any issues.
Residents in Duvauchelle, Akaroa and Takamatua were being asked to conserve water in preparation for possible stream contamination, which often happens after heavy rain and flooding.
It was less than a week since persistent heavy rain caused rivers to overflow and roads to flood and close in Christchurch.
A monster storm lashed the country for about 48 hours last week, cutting off power and causing devastating flooding in several spots over the North Island.
Christchurch City Council was forced to activate pumps as the rain coincided with a particularly high tide.