Ruapehu may erupt in the next few weeks or months, according to measurements by GNS scientists.

Scientists believe changes measured at Ruapehu during the last few weeks make an eruption in the near future more likely.

GNS Science Duty Volcanologist Steven Sherburn says they have been monitoring Ruapehu closely, but it often does not give any immediate warning that is it going to erupt.

'We think the temperature a few hundred metres beneath Crater Lake is about 800 °C, but the lake itself is only about 20 °C.

'This suggests the vent is partly blocked which may be leading to a pressure build-up beneath Crater Lake. A sudden release of the pressure may lead to an eruption.”

Since late-October small earthquakes have been occurring about 5 km beneath the summit area of Ruapehu, but these may not be directly related to the high temperatures beneath Crater Lake as the earthquakes are much deeper, says Steven.

The Aviation Colour Code has increased from Green to Yellow, but the Volcanic Alert Level remains at 1.