Magma may have been present in this week's eruption on Mt Tongariro and it is high up in the mountain, but there is no indication that a much bigger eruption is about to occur.
Scientists are continuing to monitor Mt Tongariro, which erupted on Monday for the first time in more than a century and a separate eruption on White Island, the first since 2001.
GNS Science vulcanologist Nico Fournier told NZ Newswire the discovery that there was a bit more magma in edifices on Mt Tongariro increased the likelihood of a more magmatic eruption but it was too early to assign a probability to it.
"It could range from explosions to simple lava flows but at this stage we don't have evidence that there is magma very close to the surface," he said.
There may have been magma involved in the eruption on Monday but if it was it was in very small amounts.
The discovery of magma, or molten rock, high up in the mountain did not make a larger eruption more imminent.
"At this stage simply there is no indication that there is something about to happen much bigger than what happened already and the presence of magma is not something we are surprised at.
"It is just a matter of whether it will make it up to the surface."
Earlier vulcanologist Gill Jolly told Radio New Zealand that the eruption on White Island was fairly normal and it was unrelated to the Tongariro eruption.
Multiple vents were involved in the Tongariro eruption.
Tongariro erupted about 11.50pm (2150 AEST) on Monday night, spewing ash from the Te Maari craters on the northern side of the mountain and prompting a threat warning for the central North Island.
Rocks fell within 1km of the eruption but there have been no reports of injuries.
Scientists believe the small-scale eruption, which appeared to have abated by Tuesday morning, was driven by steam rather than molten rock.