A small eruption has been recorded on White Island.
A large plume of smoke and gas is continuing to escape from the top of the coastal volcano.
GNS Science volcanologists used web cameras on the island to capture a small eruption in the early hours of Sunday morning.
GNS Science duty volcanologist Michael Rosenberg said White Island was an active volcano and small eruptions happened from time to time.
"These phenomena are not unknown for White Island, but this is the first substantial confirmation that small scale eruptions are now occurring on the island and confirms the risk to visitors has increased," he said.
The Volcanic Alert Level raised from Level 1 to Level 2 yesterday afternoon and the Aviation Colour Code was changed to Orange.
GNS Scientists have been monitoring the increasing volcanic activity for the past eight days. During this time, there has been an increase in volcanic tremors and volcanic gas levels.
An indication the volcano was about to erupt came overnight on Friday, when the lake level in the Crater Lake rose from about 3m to 5m.
Mr Rosenberg said a volcanic earthquake was recorded, which indicated an eruption may have occurred. A flow of gas and steam has been present in the lake and from vents near the lake since then.
A gas flight on August 1 recorded increased levels of sulphur gas in the steam and volcanic gas plume.
"Since early July there have been intermittent periods of volcanic tremor, becoming more continuous since July 28," he said.
"A stronger episode was recorded overnight on August 4 to 5 and ended in a volcanic earthquake at 4.54am."
The photograph was taken by Bay of Plenty Times reader Jessica Brockett from Looking Glass Gardens in Te Puke on Sunday. It shows the plume of gas which has enlarged since the crater lake level rose rapidly on July 27 and 28.
Mr Rosenberg said this had been "the first big change" at the volcano over the past two years.
He said White Island is an active volcano and there was always risk when visiting the island. He said vessels travelling nearby should keep alert.
"Eruptions can occur at any time with little or no warning. Extra caution should be taken if visiting the island."
GNS Science volcanologists are continuing to monitor the activity at the volcano.