Whakaari/White Island's Volcanic Alert Level has been raised to level 2, meaning there is "moderate to heightened volcanic unrest".
The alert was raised from level 1 to 2 by GNS Science on Monday afternoon.
In a statement, GNS Science said the change in level "acknowledged the uncertainty about what is driving current activity at the volcano".
"Persistent observations of night glow on the web cameras indicate continued emission of high-temperature gases," duty volcanologist Yannik Behr said.
"Continued decline of the carbon dioxide to sulphur dioxide ratio points to ongoing degassing of fresh magma. The Volcanic Alert Level has been raised to 2 and the Aviation Colour Code to Yellow.
"Elevated levels of gas emissions continue but the ratio of carbon dioxide to sulphur dioxide has decreased. A more detailed evaluation of this observation supports the presence of magma at shallow depth."
Behr said observation of the night glow had continued since June 30.
"There is still large uncertainty about the mechanisms driving the current activity. Most scenarios are consistent with a slightly increased level of unrest at Whakaari/White Island."
Behr said despite the change in alert level, "there are no signs of eruptive activity".
GNS has six volcanic alert levels, with 0 being "no volcanic unrest" and 5 being a "major volcanic eruption"
In late 2019 the volcano erupted while 47 people were on the island. Twenty-two people died either in the eruption or afterwards from injuries sustained in the event.