Image: NZTA
NZ Transport Agency Waka Kotahi (NZTA) advised about 2.30pm that State Highway 6 was closed between Makarora and Lake Hāwea, on the way to Haast Pass.
NZTA said the slip occurred near the Flaxmill Creek Bridge, and crews were on their way to deal with it.
"Road users are advised to delay their journeys or use an alternative route."
It comes amid heavy weather for much of the country, and downpours are expected across the divide in Westland, south of Hokitika, for the rest of the day.
MetService has an orange heavy rain warning in place for the area until 10pm.
Up to 150mm of rain is expected on top of what has already fallen and thunderstorms are possible.
