White Island volcano has erupted, prompting GNS Science to advise visitors to take extra care.

The island, located about 50 kilometres off the coast of Whakatane, is an active volcano and a popular tourist spot.

Its web camera captured the small eruption from Crater Lake, GNS Science volcanologist Michael Ronsenberg said.

"These phenomena are not unknown for While 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.

"Eruptions can occur at any time with little or no warning. We advise extra caution should be taken, if visiting the island."

GNS has changed the volcano's code from "experiencing signs of elevated unrest above known background levels" to "volcanic eruption is underway with no or minor ash emissions".

The alert level has also changed from one to two due to "minor eruptive activity".

It follows a code change last week when scientists discovered water levels in Crater Lake rose by about 3m to 5m overnight and the number of tremors had increased.

There was a particularly stronger seismic episode recorded Sunday morning, ending in a volcanic earthquake at 4.54am that day.

Rosenberg said: "[The earthquake] had a sound signal, which meant something happened on the surface. So we went back and looked at the camera images."

"Obviously being at night time, there was no visual observations and initially we weren't able to determine what that small event was.

"But we've narrowed it down and recognise that there has been full hydrothermal eruption."

Rosenberg said there had not been any further eruptions, and the number of tremors had decreased.

"It's now at similar levels to before the weekend."

GNS Science was "paying close attention" to the volcano as the last "gentle eruption" had been in early 2001.

White Island also experienced a "moderate-sized explosion" in July 2000, when fresh lava was pushed out.

"In the past this kind of activity has increased to small eruptions that produce ash, and that ash could drift as far as the mainland," Rosenberg said.

"We can't predict what the volcano is going to do and we are not making any forecasts, but yes, it's certainly possible that the activity could ramp up again."

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