The emergency Civil Defence Centre has been activated on the West Coast, with heavy rain expected to drench the region overnight.

Local emergency staff are on standby in Hokitika and additional Civil Defence staff on on their way from Christchurch and Wellington as a precaution.

Westland civil defence public information manager Andy Thompson said a large downpour of rain is expected in the next 12 hours, with up to 100 millimetres forecast.

"We're telling residents to be careful, be vigilant, just to make sure if they're driving on the roads.

"We're telling them to keep an eye on their neighbours if there's any flooding that does occur to try and keep out of that flood water as much as they can."