Mt Ruapehu's Crater Lake has nearly doubled in temperature over the past month but scientists say it is still classed as "minor volcanic unrest".
In mid-July GeoNet scientists observed the start of a typical heating cycle of the lake, Te Wai ā-moe, from a low temperature of around 14C, but had since risen to 27C.
Duty volcanologist Agnes Mazot said since the current Crater Lake was established in 2003, they had observed typical heating and cooling cycles where temperatures ranged from 12 to 40C over 12 months.
The current level of activity was consistent with that minor volcanic unrest behaviour that had characterised Ruapehu throughout the past 16 years.
The Volcanic Alert Level remained at 1.