The Department of Conservation has re-drawn a 700-metre exclusion zone around Ruapehu, asking Kiwis not to visit Crater Lake.
In response to a GeoNet bulletin on Tuesday, DoC is advising visitors not to camp or stay overnight within 1.5 kilometres of the summit lake.
Tuesday's bulletin advised that the volcano has entered a "heating phase" with the lake temperature reaching 31 degrees Celsius. The volcanic lake goes through periods of heating and cooling.
While these are within normal ranges of fluctuation, the area remains at Volcanic Alert Level 1 or "minor volcanic unrest."
"Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest," said GeoNet volcanologist, Craig Miller.
The exclusion area should not affect any visitors' planned activities to the Tongariro National Park over summer but should serve as a reminder that the volcano could become active at any point.
The Department of Conservation said this recommendation area does not affect any tracks or facilities in Tongariro National Park.
The area of avoidance from the centre of Te Wai ā-moe is DoC's "normal recommendations to visitors at Ruapehu" under the alert Level 1, said a department spokesperson.
"DoC operates a robust volcanic risk management system in Tongariro National Park. This system informs how we respond to changing unrest conditions at the volcanoes and manage risk to the public."
The volcano remains one of just two volcanoes in the country above level zero, alongside Whakaari/White Island, which is currently at Level 2.
The volcano last erupted Fifteen years ago in September 2007, causing two lahar earth flows down the mountain and a seven-minute earthquake recorded nearby.
In September this year, there was a false signal detected from the Eruption Detection System on the mountain.
On 23 September the Ruapehu warning system was triggered by an offshore earthquake resulting in a warning issued for the Whakapapa Ski area.
"These conditions perfectly mimic an eruption and it performed as designed," said DoC.