White Island has been spewing mud and rock several tens of metres into the air in the past few days, as GNS Science warns of a greater risk to visitors.
Scientists monitoring the island volcano in the Bay of Plenty say the crater lake is drying out and the frequent bursts of mud, steam and gas were still vigorous.
The continuous volcanic tremor at White Island had also changed to a pattern of intermittent tremor.
"During the last few days, the bursts have thrown mud and rock several tens of metres out from the lake area. Steam and gas clouds above the volcano are often visible from the Bay of Plenty coastline," said GNS Science.
Past monitoring showed that weak ash eruptions had often followed the drying out of the lake.
"More vigorous explosions of mud, rock and perhaps molten sulphur are possible in future with little or no warning."
The amount of volcanic gases measured last week were similar to those measured in December and did not suggest a large eruption was imminent.
However, White Island was still at an elevated state of unrest.
The current episode of activity on New Zealand's most active volcano began in August last year, with explosions and ash emissions, followed by the appearance of a small lava dome in November.
The volcanic alert level remained at one and the aviation colour code remained at orange.
White Island Tours spokesman Patrick O'Sullivan said tours to the island were still operating.
"We have still been operating this whole time, it hasn't really affected us as yet. We just are taking extra precautions when we're out there,'' he said.
An extra guide would scout ahead of the tourist party, and they would only stay near the crater area, where most of the thermal activity was, for a maximum of five minutes.
Mr O'Sullivan said tourists who visited the island were excited by the activity, and it was hard to move them on from the main crater area.