Because of bad weather in the area, the fly-over was unable to get close enough to the mountain to determine the impact of the eruption immediately around the craters.
He also could not confirm from which crater the eruptions occurred but anecdotal evidence suggested it was Te Mari.
"In the 12-14 hours before the eruption there was no increase in activity," he said. "Similarly, there had not been any action since the eruption."
Changes in volcanic gas levels had been recorded in the past few weeks, but there was not any significant increase leading into the eruption.
Mr Scott described the eruption as "small scale", and he would not be surprised if there were more small-scale similar eruptions.
"I would really love to be able to tell you what is going to happen next, from the seismograph information we're not seeing an escalation, we're not seeing more energy being released, and we didn't see a whole pile of energy being released before the eruption started.
He said if the unsettled activity continued a molten eruption could develop.
Inspector Brent Crowe from Bay of Plenty police said the focus for police was on public safety and reassurance.
He said two teams were yesterday morning on the mountain checking huts and tracks for people, who would have to be evacuated.
He said the wider community was not currently at risk in terms of health.
"There is no need for the wider community to remain inside and close doors and windows.
"At this time the only risk is minimal and would only be to people in the local vicinity of the eruption who have a predisposition to respiratory issues. The only other advice is in relation to water supplies of the rural community in the immediate local area."
Nic Peet from DoC said all huts, tracks and the Tongariro Crossing were closed and officials were not sure when they would be reopened.
The Turoa and Whakapapa ski fields are not affected and are open.
Mr Peet said there were no records kept of how many people were on Mt Tongariro on Monday night, but three people were yesterday morning evacuated from the Mangatepopo Hut.
Bubs Smith said Tuwharetoa had moved some "at risk" residents.
He said 24 people were moved to a Turangi Marae about 12.30am after the alarm was raised about the eruption. Those who had been evacuated to the marae were mainly elderly residents and those with small children, who could be vulnerable to the ash.
Mr Smith said the community was prepared for such an occasion and everyone was staying calm.
Meanwhile ash from the Mt Tongariro eruption lead to the cancellation of the 7.05am Air New Zealand Rotorua-to-Auckland flight yesterday. An Air NZ representative at the airport said all other flights were running to schedule and passengers on the cancelled service had been moved to later flights.
Visit www.dailypost.co.nz for video footage of yesterday's press conference.