"Significant rain" has fallen overnight in the Westland District after flooding washed away Waiho Bridge and slips closed roads.

A state of emergency was declared yesterday after the Waiho Bridge was completely destroyed last night.

Some parts of Westland had up to 800mm of rain during the downpour and the town of Haast is experiencing a one-in-100-year flood.

Seven people have been evacuated from their properties in Waiatoto and a welfare centre at Haast is opened.

Preparations were made in case parts of Hokitika needed to be evacuated but that was not required as water levels receded at high tide, Civil Defence said.

Aerial inspections will take place this morning to assess the extent of damage, and the rain is moving north, it said.

State Highway 6 is closed between Hokitika and Makarora, and a slip at Candys Creek on SH73 on the Arthur's Pass/Otira route between the West Coast and Canterbury has closed the highway. It will be reassessed about 8am.

Civil Defence West Coast's Facebook page has more information about local road closures] and the Transport Agency about the state highway system.