A slip of trees, soil and rocks nearly half a kilometre long has closed the main highway heading to the West Coast's glaciers.

It was estimated to be close to 400 metres in length and cascaded down over State Highway 6 north of Franz Josef Glacier.

"Given the depth of material with large trees, soil, rocks and streams cutting across the highway, it is unlikely to be reopened until early next week, says Moira Whinham, Maintenance Contract Manager ar NZ Transport Agency.

Electronic signs advise drivers of the closure at either end of the highway – just south of Hokitika at the top of the road as well as Makarora and Lake Hawea at the Otago end.

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Crew and equipment have been on the site since the early hours of this morning and more equipment and people are heading to South Westland to clear the slip.