DoC is advising visitors not to enter Ngauruhoe's crater area.
Trampers have been warned to stay away from Mt Ngauruhoe's crater after an increased number of tremors beneath the volcano.
Scientists have raised the active volcano's alert level from 0 to 1 after seismographs on the Tongariro National Park mountain recorded a significant increase in the number and size of
earthquakes in recent weeks, although that does not mean an eruption is imminent.
The Department of Conservation is advising visitors not to enter Ngauruhoe's crater area, in case there are increased concentrations of volcanic gases, which could make breathing difficult.
DoC scientist Dr Harry Keys said this was a precautionary measure while volcanologists from crown research institute GNS Science stepped up their monitoring of Ngauruhoe, which last erupted in February 1975.
"This is standard practice for volcano management," he said. "There's been a first sign of unrest picked up but there's nothing to indicate we should close the Tongariro crossing track facility. We will keep monitoring it."
The volcano alert level system ranges from 0 to 5, with 5 being the most serious.
Mt Ruapehu has been on alert level 1 since October 1997. It erupted in 1995
"The question is what it's likely to do over the next period and there's a number of scenarios," Dr Keys said. "GNS Science haven't yet got sufficient information to make any call on which is the most likely scenario from here."
Four portable seismographs will be placed on the mountain tomorrow so scientists can better assess volcanic activity.
DoC is in close contact with GNS Science and will update its advice as more information becomes available.
Ngauruhoe is visited by a small number of the 65,000 people a year who use the Mangatepopo Valley route to the Tongariro crossing.
MT NGAURUHOE
* The youngest vent on the Tongariro volcano system
* Its last major eruption, on February 19, 1975, sent debris and ash 10km high
* Ngauruhoe is thought to have first erupted just 2500 years ago
