There has been a large landslide at Omoto, east of Greymouth, closing a section of the highway until at least Tuesday.
Continuous heavy rain and high river levels have contributed to the 2.5 metre landslide drop overnight east of Greymouth on State Highway 7, between Greymouth and Stillwater, an NZ Transport Agency spokesperson said.
A short road detour is available just across the Grey River via Taylorville.
The highway will remain closed at Omoto until at least Tuesday morning given the recent movement, said Moira Whinham, maintenance contract manager for the Transport Agency on the West Coast.
In the last week the highway was re-opened to a single lane with traffic management, subject to weather and safety considerations.
Yesterday's rain had seen the slip accelerate and drop by more than two metres overnight, Ms Whinham said. The highway was closed yesterday at 5pm.
She advises road users to take it slowly on the local road detour, particularly through Taylorville.
The detour route is via Taylorville, with the turnoffs at Stillwater and Cobden bridges on the north side of the Grey River.