The Department of Conservation says the top of Mt Ruapehu will be off-limits for some time as pressure builds within the central North Island mountain.
GNS Science says it looks inevitable that the mountain will erupt in coming months due to a vent being blocked.
A number of earthquakes have also been recorded on the mountain over the past few weeks.
DoC's volcanic risk manager Harry Keys told Radio New Zealand's Morning Report programme on Monday that people should not go up to the summit hazard zone, about 2km from the centre of the crater and above the Whakapapa ski area, for the foreseeable future.
The department will review the warning regularly depending on the volcano's activity, he says.