Eruptions at White Island are possible with little or no warning, as seismic activity increases.
Scientists and Bay of Plenty Civil Defence staff have been keeping a watch on White Island this weekend after GNS scientists noticed the type of seismic activity at the volcano had changed.
While the level of volcanic tremor began to decrease, hybrid volcanic earthquakes associated with the movement of magma had appeared.
GNS scientists took a gas flight over the volcano on Friday, which showed a level of gas emitted was similar to last month. Mud geysering is continuing in the crater lake and earthquake activity remains above background levels.
Civil Defence Emergency management group controller Warwick Murray said the current episode of activity started in August 2012, with explosions and ash emission, and in November, a small lava dome appeared.
He said volcanic unrest had been increasing since about January 14.
"Increased hydrothermal activity in the 'hot lake' has been described as some of the most vigorous seen for many years. Future eruptions are possible with little or no warning, meaning an increased hazard to visitors to the island."
Hazards could include the health effects of volcanic gas exposure, respiratory issues, skin and eye sensitivity to acid gases.
"A high level of caution should be taken if you are visiting White Island. Scientists are not sure what could happen next - magma could flow underground with no changes in surface activity, there could be more dome building, as in November; or explosive eruptions and ash emissions, as in August last year," he said.
While people were becoming concerned with the level of activity on the island, Mr Murray said there was little risk to the mainland from this seismic activity.
"Visitors to White Island should ensure that they informed and must exercise high level of caution. If you are boating near the island throughout the long weekend, monitor marine channels for updates and exercise caution."
Meanwhile, the Volcanic Alert Level for White Island remained at 1, indicating signs of volcanic unrest and the Aviation Colour Code has been lifted from yellow to orange.