Scientists aren't ruling out an eruption on Mt Ruapehu, as the temperature of its crater lake soars.
The lake water has reached 44degC -- a 16-year high -- and a series of volcanic quakes and tremors have also been recorded this month.
Volcanologist Brad Scott says monitoring has been stepped up, but there's no cause for alarm yet.
He says Mt Ruapehu is an active volcano and it's erupted while the lake has been both hot and cold.
"Over the last two weeks it's been heating quite dramatically, about 1degC a day, and temperatures have risen now to about 44degC.
"There have been lots of times in the past when the lake's heated up and no eruptions have occurred, but there are also some examples of when it has, so there's not strong definitive rule unfortunately."