Slips and flooding have closed the main highway in several places in the southern West Coast.
MetService is warning of heavy rain for much of the region today, though the terrible weather predicted for this weekend a few days ago has since been downgraded.
Police say parts of State Highway 6 in south Westland are shut.
West Coast Civil Defence have opened an emergency operations centre in Hokitika as a precaution, and will open another in Greymouth this evening as the weather moves north.
MetService said up to 200mm would fall in Westland north of Otira and up to 150mm in the Buller District.
Emergency Management Group Controller John Canning said the modelling showed the system moving north over the day.
The forecaster warned heavy rain could cause rivers and streams to rapidly rise, and surface flooding was likely.
Canning said 15mm of rain an hour was expected in Greymouth this afternoon, and it was worth being prepared.
"It's fairly changeable but we're not having heavy rainfall at present so we're gearing up, if it does get heavier, for flooding in the townships on the coast. And hopefully we can deal with that.
So far, emergency services had not had to deal with any flood-related issues.
Surface flooding was expected in Buller overnight.
Residents and drivers were asked to take care due to slips and surface flooding on roads, and keep an eye on the West Coast Civil Defence's Facebook page for updates.