Volcanic activity at White Island is increasing and future eruptions are possible with little or no warning, say scientists who have increased the volcano's alert level.

GNS Science will undertake a flight over the island this morning to assess the level of activity after hybrid volcanic earthquakes began to appear resulting in an increase in the Aviation Alert Code.

White Island - about 49km off the Bay of Plenty coast. Photo: Geonet.

The White Island crater floor taken at 8.30am today.

GNS volcanologist Gill Jolly says the increased level of unrest does mean that there is an increased hazard to visitors.

'Visitors to White Island are now at the highest level of risk since the start of the 2012 eruptions,” says volcanologist Gill Jolly.

'Hazards to visitors can include the health effects of volcanic gas exposure, including respiratory issues, skin and eye sensitivity to acid gases. Explosive eruptions can occur at any time with little or no warning. We advise a high level of caution should be taken, if visiting the island”.

GNS first reported increased activity on Tuesday which has changed in the last day.

The aviation alert code has now been raised from yellow – the volcano is experiencing signs of elevated unrest above known background levels – to Orange meaning the volcano is exhibiting heightened unrest with increased likelihood of eruption.

The level of volcanic tremor has started to decrease, but hybrid volcanic earthquakes have appeared. Hybrid earthquakes are a mix of rock fracturing and magmatic vibration, and are thought to represent the movement of magma in a volcano.

The current spate of activity began in August 2012 with explosions and ash emissions, followed in November 2012 by extrusion of a small lava dome. Elevated but not high activity followed.

White Island has become more active since January 14 with increased hydrothermal activity in the ‘hot lake' described as some of the most vigorous activity seen at White Island for many years.

But scientists still say things could go either way. The magma could rise to shallow depths with no changes in surface activity, and more dome building as in November 2012, or their could be explosive eruptions and ash emissions, like in August 2012.

A ‘gas flight' is to be made this morning to see if there have been any changes in the gas flux from the volcano.

Aviation Colour Codes are based on four colours and are intended for quick reference for pilots.