A recent increase in seismic activity around the central North Island volcano Mount Ngauruhoe has seen the mountain's alert level raised.

GNS Science has raised Ngauruhoe's alert level to one, matching the levels of nearby volcanoes Mount Ruapehu and Mount Tongariro, as well as White Island in the Bay of Plenty.

Mount Ngaruahoe is at Alert Level One.

'During the last two to three weeks there has been an increase in the number and magnitude of earthquakes being recorded by the GeoNet seismographs around Mount Ngauruhoe,” says duty volcanologist Art Jolly.

'Initial analysis indicates these earthquakes are shallow, occurring at depths of less than about five kilometres.”

Ngauruhoe's alert level was raised late yesterday after seismic activity increased above the typical background level, indicating minor volcanic unrest.

The last significant eruption at Ngauruhoe was in 1975. Earthquakes are not unusual near Ngauruhoe, but it is some time since GNS Science last recorded significant numbers or events above magnitude one, says Art.

Similar numbers, but smaller events occurred in December 2014. Other swarms of earthquakes near Ngaruahoe occurred in 1983, 1991, 1994, 1995 and again between 2006 and 2010.

Its volcanic alert level was raised to level one in June 2006 and then lowered to level zero in December 2008 in response to earthquake activity at that time. No other measured parameters, including gas and temperature, changed during these times.

'The current change at Ngaruahoe indicates the volcano has entered a state of volcanic unrest, like we have recorded several times in the last 30 years,” says Art.

'No previous periods of unrest have resulted in a volcanic eruption. The outcome of this unrest is more likely than not that there will be no eruption in the short term, like during the 2006-2010 unrest.”

Ngauruhoe will be closely monitored and GNS Science will release updated information as it is available or necessary.

The Volcanic Alert Level ranges from zero to five and defines the current status.

The Aviation Colour Code for Ngauruhoe is Green. Aviation Colour Codes are based on four colours and are intended for reference only in the international civil aviation community.