Volcanologists say Whakaari / White Island is currently emitting larger steam and gas plumes than normal — however, no ash has yet been detected.

Volcanologist Yannik Behr of GNS said scientists had noticed a "general increase in sulphur-dioxide emissions from the volcano" seen above the island, 48km offshore of Whakatāne, over the past two weeks.

A Volcanic Alert Level 2 remained in place, indicating moderate to heightened volcanic unrest, and the Aviation Colour Code remained at Yellow.

Behr said the larger steam and gas plume was seen on webcams and satellite images on December 10, and on clear days could also be seen from the Bay of Plenty coast above the island.

"During our latest monitoring flight on December 5, we did not observe any signs of increased volcanic activity. There were no signs of new ash deposits in the crater or the island," Behr said.

He said the plume was "vivid white, consisting of steam and gas, with no signs of ash entrainment".

The temperature of the plume, measured with a thermal infrared camera, was a "relatively cool" 150C.

Behr said GNS Science's Volcano Monitoring Group and National Geohazards Monitoring Centre would continue to closely monitor Whakaari / White Island for any changes in activity.

"It is possible that the increase in SO2 emissions and size of the plume could be related to fresh magma getting closer to the surface, as it did a few months ago.

"But so far, no ash seems to have been emitted at the surface."