A massive slip of trees, rocks and soil has come down covering almost half a kilometre of the main trunk line to the West Coast's glaciers.

The landslide estimated to be around 400 metres long cascaded down over State Highway 6 between Harihari and Whataroa on Thursday evening.

The area was hit with 180mm of rain causing the land to give way, blocking the northen access to Franz Josef Glacier and Fox Glacier.

Whataroa acting fire chief Ian Philips told Newshub two vehicles with five people in them became wedged between two sections of the major landslide.