Seismic activity on Mount Ruapehu is increasing as the temperature of the crater lake steadily rises.
The lake has been heating at a rate of about one degree per day since early September, reaching a maximum of 40 degrees Celsius at the beginning of October.
The temperature had since cooled slightly and was now hovering around 37°C.
GNS Science said the level of volcanic tremor under the mountain had increased in strength and remained higher than normal.
The volcanic alert level remained at level one, which means minor volcanic unrest, GNS Science said.