An eruption of Mount Ruapehu is more likely than normal, with heightened levels of unrest being monitored, GNS scientists say.
Monitoring was still showing higher than normal temperatures beneath the volcano's crater lake, GNS Science head vocanologist Gill Jolly said.
"We think this reflects a partially sealed zone a few hundred metres beneath the lake which might be causing a pressure build up behind it. That pressure would make an eruption more likely than normal," she said.
An eruption was not inevitable, Dr Jolly said.
"If the sealed zone fails suddenly an eruption could occur, probably with little or not warning.
"If it fails more gradually then the pressure would probably be released more slowly and the likelihood of an eruption would revert to normal."
Dr Jolly said scientists never had the whole story in regards to what was happening with volcanoes so assessments were always uncertain.
"It's like detective work without all the clues.
"But when we see something that might increase the chance of an eruption we have to be more cautious."