The Department of Conservation (DoC) says the rockfall in the Southern Alps on Monday was the largest in more than 20 years.
The giant rockfall from a mountain near Aoraki/ Mount Cook missed a trampers' hut by less than 200 metres.
The rockfall happened shortly after 2pm on Monday and was about 3000 metres long. It came to rest near the Plateau Hut which had 15 people in it at the time.
DoC spokesperson Shirley Slatter said the last significant rockfall in the Alps was on Aoraki/ Mount Cook in 1991.
Ms Slatter says a geologist will survey the mountain on Tuesday to determine the cause and when the hut can be safely reopened. Climbers should assess the risks and make their own decisions on whether to climb the mountain.
The Mountain Safety Council says Monday's rockfall has not increased the risk of climbing in the Southern Alps.
Alpine and avalanche programme manager Andrew Hobman says people can continue to climb in the area, but should always take care in alpine conditions and heed any warnings or forecasts.