Road repair crews are working hard to restore the flood-damaged State Highway 6, as West Coasters face a 1000-kilometre detour to get to Queenstown

The highway north of Makarora has been closed since Thursday.

Torrential rain swept away mud and debris from a slip across a kilometre of the highway at Muddy Creek.

Waka Kotahi says at least 20,000 cubic metres of material has to be removed before the road can re-open.

Debris at the bridge is up to four metres deep and turned "concrete hard" by subsequent snowfalls.