Greymouth has been hit by large-scale surface flooding after heavy rain on Thursday morning.
The rain is causing "significant issues", with reports of houses being flooded and roads closed.
"If you need to leave your property, people are welcome to go to the welfare centre set up at the Westland Recreation Centre, High Street," the council says.
NIWA reports that over 153mm of rain has fallen in Greymouth in the past two days. MetService says about 75mm of rain fell on Greymouth in just two hours today.
Footage shows streets washed under water, leaving cars stranded. There are slips across roads, which have been left covered in debris.
MetService has issued a severe weather warning for Westland and Buller, as well as Canterbury High Country within 10km east of the main divide.
"A complex trough of low pressure affects the South Island through to early Saturday. This system will continue to bring rain to central and northern parts of the South Island, with outbreaks of heavy rain in Westland and Buller and parts of Canterbury High Country," it warns.
"The heaviest rain should fall between Seddonville and Haast until Friday morning, and a heavy rain warning is in force.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."