Mount Tongariro has been rattled by numerous small earthquakes in the past few weeks, which could spark an increase in volcanic activity, GNS Science says.
Volcanologist Michael Rosenberg said scientists had been unable to pinpoint the location of the quakes because they were so small in magnitude.
"What we can say is that they're located somewhere underneath the mountain and for that reason we are paying particular attention to them.''
There had been about 10 quakes measuring less than one in magnitude over the past two weeks, Mr Rosenberg said.
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"But they're unusual because in the last six months or so we've had virtually none and the fact that they're underneath Tongariro makes us pay close attention to the other parameters that we monitor, just in case they're a precursor to some volcanic unrest.''
Scientists had not seen any changes in volcanic gases, which meant that while the earthquakes were important, they were not acting as a major warning yet.
The amounts of carbon dioxide and sulphur emitted from Tongariro have remained at low levels since the start of this year and are about half the amount produced after the November 2012 explosion, Mr Rosenberg said.
These conditions, and the small number and small size of recent earthquakes are not sufficient to alter the unrest status of the volcano and GNS Science has not changed the Volcanic Alert Level from 1, indicating signs of unrest, or the Aviation Colour Code from Green.
"It's certainly no cause for immediate alarm,'' he said.
"People will appreciate that Tongariro is an active volcano and there's always a certain amount of risk associated with that, but these earthquakes don't change that (risk).''