Mt Tongariro's alert level remains at level one, despite earthquake activity below the volcano falling over the weekend.

The volcanic alert level was lifted for Mt Tongariro after a series of small earthquakes were recorded beneath the central North Island mountain on July 13.

They died down but flared up again on July 18 and increased in frequency on Thursday and Friday.

GNS vulcanologist Brad Scott said the small earthquakes were all below magnitude 2.5, but the increased activity appeared to have slowed over the weekend.

Scott said although the quakes were small, Geonet had increased monitoring due to their frequency.

Latest earthquake drum charts showed some movement over the weekend, but Scott said it was not significant and was most likely caused by rough weather.

"It goes to show how sensitive the instruments are. Whenever there is rough weather the signal gets transferred through the ground and it does show in the charts."

Seismic data had shown that small volcanic earthquakes were common at Mt Tongariro, but usually only occurred at an average rate of two per year.

More than 20 had been recorded since July 13.

Seismic activity indicating unrest was last detected on the mountain during 2001.

"Our routine volcano monitoring also includes the chemistry of the lakes, springs and fumaroles on Tongariro,'' Scott said.

GNS Science had upgraded the volcanic alert level from zero to one, which meant activity had risen from "typical background surface activity".

Level two signalled minor eruptive activity and level five indicated a large hazardous eruption in progress.

Mt Ruapehu and White Island each have an alert level of one.

The aviation colour code was also upgraded for Mt Tongariro from green to yellow, meaning the volcano was experiencing signs of elevated unrest above known background levels.

Mt Tongariro was made up of multiple volcanic cones constructed over a period of 275,000 years. There have been five reported eruptions from Te Mari craters and Red Crater between 1855 and 1896 and these have since been dormant.

- © Fairfax NZ News