Increasing unrest on White Island has seen the aviation colour code lifted to orange.
GNS volcanologist Gill Jolly said visitors to White Island were now at the highest level of risk since the start of the 2012 eruptions.
"Hazards to visitors can include the health effects of volcanic gas exposure,including respiratory issues, skin and eye sensitivity to acid gases. Explosive eruptions can occur at any time with little or no warning."
A high level of caution should be taken if visiting the island.
Ms Jolly said the style of seismic activity at the island had changed during the last day.
The level of volcanic tremor had started to decrease, but hybrid volcanic earthquakes had appeared.
Hybrid earthquakes were typically associated with the movement of molten material (magma) within an active volcano.
The current episode of activity started in August 2012 with explosions and ash emission and was followed in November 2012 by the extrusion of a small lava dome.
