Increased volcanic activity on Whakaari / White Island will be closely watched by experts from the air on Monday.

There has been a string of eruptions there in recent days, and the alert level remains at three out of five.

It was raised to three after its webcam at Whakatāne captured footage of intermittent "energetic ejections of steam and gas" starting on Friday.

GNS Science says cloud over the island has made monitoring difficult, but scientists still think the volcano is in an eruptive period.

The volcanic activity does not pose a threat to the mainland.

GNS volcanologist Geoff Kilgour says two eruptions were seen on Saturday - one at 8am and another around midday.

For the past 20 years or so, Geoff says the island has seen a series of eruptions every three to five years, and the activity being seen may mean "we are entering one of these eruptive phases".

Experts would be conducting a flight over the island at about 10am to see the gases that have been emitted and what it happening on the island itself.

Activity was currently "very minor" with eruptions only impacting the island itself and its very near surrounding.

The height of the plume was only two kilometres, which was considered low.

Geoff says the 2019 deadly eruption had degraded its sensors on the island so GNS Science relied on observation flights and satellite information to make up for the loss of information on the island itself.

Advice for boaties remained that they should stay away from the island's direct surrounds.

-RNZ