The Department of Conservation is worried someone will be killed as giant chunks of ice are falling from rapidly advancing glaciers in the middle of the peak visitor season.
Staff believe the risk of ice collapse at the face of the Fox and Franz Josef Glaciers is high and visitors are ignoring warning signs and putting themselves at risk.
Both glaciers are advancing at the rate of about a metre a week.
Fox is pushing up the sides of the valley, stressing the terminal face and causing rock falls and ice collapse.
The Franz Josef terminal face is moving over a section of rock that is raising it up and causing pressure that will release as it crosses the highest point of the rock, significantly increasing potential hazards.
Up to 1000 people are visiting Fox Glacier daily, and 2700 Franz Josef.
DoC staff say people are ignoring the warning signs and crossing the rope barriers to get closer to the ice caves and rivers.
They say tourists seem unaware that what appears to be a static block of ice is actually dynamic and changing all the time.
Fox guiding co-ordinator Kerie Uren said large groups, including families with children, were daily crossing the rope barriers and putting themselves at extreme risk.