There's ''significant concern'' that increased volcanic unrest at White Island could be the precursor to more extreme activity and it could erupt at any time.

Volcanologist Brad Scott visited the island off Whakatane yesterday and said the hydrothermal activity is some of ''the most vigorous'' he's seen for many years.

''This type of activity usually leads to stronger volcanic activity and is a significant concern," Mr Scott said.

His observations, released in an alert bulletin, confirmed that hydrothermal activity in the small hot lake has increased. 

The most common activity is "doming-up" of the lake surface by steam and gas that brings large amounts of sediment to the surface.It often co-coincides with vivid white steam/gas ''flashing'' from around the base. 

Every so often stronger events happened.This activity has been increasing since late 2012 and is now semi-continuous.

The lava dome that was first observed in late November has not changed since the last observations on January 1, 2013.

There are elevated levels of volcanic tremor and this is likely to be generated by the processes driving the vigorous hydrothermal activity in the lake.

The state of unrest at White Island is increasing and future eruptions are possible with little or no warning. 

The increased level of unrest does mean that there is a hazard to visitors.

Past activity indicates that eruptions, such as that which occurred on 5 August 2012, could occur with little or no warning, even when the Alert Level is 1 (volcanic unrest).

Caution should be exercised when visiting the island.

The aviation colour code remains at yellow - volcano is experiencing signs of elevated unrest above known background levels.

GNS Science continues to closely monitor White Island through the GeoNet project.

- © Fairfax NZ News