A White Island eruption looks increasingly likely, with increased signs of volcanic activity and nearly continuous tremors.
The aviation warning for the island, that lies 50km of the coast of the Bay of Plenty, has been upgraded to orange, the second-highest alert level.
It means the volcano is experiencing heightened unrest and the likelihood of an eruption has increased.
Yesterday GNS Science volcanologist Gill Jolly said the level of volcanic tremor had decreased but that there had been an increase in hybrid earthquakes, which were typically associated with the movement of magma within an active volcano.
Scientists will be flying over the volcano today to see if they can determine if a large eruption is imminent, but they've already said one could occur with little or no warning.
Hazards to visitors included volcanic gas exposure, including respiratory issues, as well as skin and eye sensitivity to acid gases.