Vulcanologists say molten rock appears to be moving higher inside Mt Ruapehu, but it is unclear whether the mountain is about to erupt.
"Elevated gas output, high lake temperatures and a volcanic tremor continue to indicate elevated `unrest' at Ruapehu," GNS Science warned today.
"It is unclear if this is a sign of further eruption in the near future."
Eruptions in 1995 and 1996 wrecked the ski seasons in those years and were economically disastrous for the area, helping to drive the Turoa ski resort into receivership after a bad snow season in 1998.
GNS scientists have monitored the mountain closely since a moderate-sized steam eruption in the crater lake last September.
Auckland teacher William Pike lost part of his leg after a lahar smashed through Dome Hut, near Ruapehu's summit, pinning him under a wave of debris.
No further eruptions have occurred, but skiers and other visitors were warned last month that an increase in gas output and the internal temperature of the volcano represented an "anomalous state of activity".
Today, the scientists said that the sulphur dioxide in the gases discharged from the volcano have gradually increased since last year's eruption, and the sulphur dioxide and carbon dioxide emissions were now about 10 times the normal background levels.
The Crater Lake temperature has been fluctuating between 34degC and 36.8degC - temperatures which require sustained heat from deep in the volcano.
The crater lake temperature goes up and down every nine to 15 months, but it has been hovering around in the 34-38degC range when it normally would be lower.
"The source of this heat is magma within the volcano conduit," they said. "This magma is also producing the higher-than-normal gas flow."
The mountain remains on alert level 1- the lowest is zero, the highest five - and further checks on water temperature and gases will be made this week.