Volcanic White Island has erupted with "some kind of burp" in a small event signalling a change in the nature of its activity, GNS Science says.
The island, off the Bay of Plenty, has shown increased activity this week, but on Tuesday tremors dropped sharply about 11.30pm.
"It is unclear if there was an explosion associated with it - there is some acoustic signal on our instruments, however it's not clear if it is wind noise or not," duty volcanologist Craig Miller said in a statement.
There was another short burst of tremors around 3am on Wednesday and another acoustic signal.
"The Crater Rim camera appears to be splattered with mud/ash this morning so it seems there has been some kind of burp," Mr Miller said.
The plume out of the crater lake, seen from a monitoring camera, also appears darker and maybe more ash rich.
"It appears the nature of activity at White Island might be changing somewhat," Mr Miller said.
On Sunday, GNS cameras captured photographs of a small eruption at Crater Lake.
The alert was raised from one to two on a scale of zero-five. White Island consistently sits on alert level one.
During the past fortnight there has been an increase in volcanic tremors, volcanic gas levels and the crater lake water level rose 3m to 5m.
GNS says White Island's activity is not linked to activity on Mt Tongariro, where there was a small eruption on Monday night.
NZN