Unsettled activity at White Island, which has prompted authorities to raise alert levels, indicates the volcano could erupt at any moment.
But exactly if, when, or how that may occur remains unclear as scientists gather more data from the off-shore Bay of Plenty volcano, which has been in an eruptive cycle since last August.
Over previous months, a jagged lava dome plugging magma below has emerged in the volcano, which is New Zealand's most active.
Hydrothermal activity had also seen large amounts of sediment coming to the surface, often with vivid white steam and gas flashing from around the base of the volcano's lake.
Discussing potential scenarios, GNS head of volcanology Dr Gill Jolly said the unrest could result in explosive activity, extrusion at the volcano's lava dome, or nothing at all.
"It's quite hard to tell which of these scenarios is most likely and we are collecting more data,'' she said.
An eruption would likely have little or no impact on the mainland 48km away - nearly all previous eruptions had only affected the island itself - but under certain wind conditions, a light ashfall could carry a fine layer of pollen-like ash.
Scientists were flying over the island today to collect further data and make visual observations.
Dr Jolly described volcanoes as "fickle beasts'' and it was entirely possible White Island could catch scientists off-guard, as happened at Mt Tongariro in August and November last year.
"They often look like they're building up to something and then nothing happens at all,'' she said.
"It's very important for us to monitor very regularly and assess the daily activity.''