Hawke's Bay people are being advised that the volcanic eruption threat has passed for now but volcanologists say the elevated level of risk remains.
A brief eruption late last night on Mt Tongariro resulted in a sizable fine ash cloud dispersing across Hawke's Bay, and particularly in the north-west of the region. A layer of ash approximately 1mm in depth came to ground inland from Napier and north-east into the Wairoa area.
Hawke's Bay Civil Defence said the latest assessment from GNS Science was that eruption activity is low level.
"It is too early to predict the next series of events, but GNS Science expects heightened activity may continue for several weeks. The volcanic alert level for Tongariro volcano remains at alert level 2."
Hawke's Bay CDEM Group Controller Ian Macdonald is urging people to ensure they are prepared in case of a further eruption and potential evacuation.
"People should have a getaway kit ready and emergency survival items to cope on their own for three days or more," says Mr Macdonald.
"In particular volcanic activity can result in lengthy power cuts and people should make sure they have stocked up on torches and batteries and should be prepared to cook without electricity."
The eruption caused all flights in and out of Hawke's Bay airport to be closed today, postal deliveries were cancelled due to the potential risk from ash fallout and many residents have a fine coating of ash on their cars.
The aviation colour code around Mt Tongariro has been downgraded from red to orange, but the volcanic alert level remains where it was after the mountain burst into action last night.
Shortly after midday today GeoNet downgraded the aviation colour code, but it has maintained the volcanic alert level at 2.
GeoNet this morning said the plume from the eruption last night was steam-driven, coming from the hydrothermal system rather than from new molten lava rising to the surface.
It shot almost 7000m into the air, ``which is not insignificant'', Civil Aviation Authority manager of meteorology Peter Lechner said.
The plume was now sitting over the volcano and to the east towards Hawkes Bay.
``So that block of plume is just quietly drifting away to the east where it will be right off the coast later this evening,'' Mr Lechner said.
GeoNet spokesman John Callan said the seismic activity had died away, as well as the steam plume.
The downgrade of the colour code - which is used to alert aviation operators to activity around a particular volcano - was because there was less ash in the air and the plume was much smaller.
However, it was difficult to predict what would happen next.
``It is too early to predict the next series of events, but we expect heightened activity may continue for several weeks. There are likely to be specific signals of future magma movement beneath the volcano and we continue to monitor the situation through the GeoNet volcano-seismic network of instruments,'' GeoNet said in a statement.
``As with any volcano, an eruption could occur at Tongariro at any time with little or no warning and there is an elevated level of risk, particularly on the northern slopes and valleys of the mountain.''
The aviation colour code uses a traffic light system to alert aviation operators to volcanic activity.
Orange means the volcano is experiencing heightened unrest with increased likelihood of an eruption, while red means eruption is forecast to be imminent.
The volcano alert system rates volcanic activity from zero to five - with zero meaning it was usually dormant and seismic deformation and heat flows were at a low level, while five meant there was a large hazardous eruption in progress.
Level 2 means there is minor eruptive activity.
Helipro pilot Toby Clark took a group of scientists up Mt Tongariro at first light this morning to evaluate the situation.
Bad weather made it difficult to get up to the mountain, but Mr Clark eventually found a space in the weather to the west.
Once above the mountain it was difficult to see because it was covered about 90 per cent by cloud.
``We were able to see the ash plume, or part of the ash plume that was coming up through the cloud, so that was extending up to about 9000 feet.''
They also flew down to check that one of the Department of Conservation huts did not have people in it.
``To be fair, we didn't manage to see the origin of the eruption or the crater.''
The scientists on board were a bit disappointed that they could not see the origin of the eruption, he said.
``But they were pretty happy to see that there was activity there and that it was coming from the area that they thought it was.''
Mr Clark had flown up around the Mt Ruapehu eruption in 1995.
``This, in the GNS words, is nothing like the event of Ruapehu. It was a relatively small event at the moment, but they wouldn't be drawn to the fact that it potentially could go again, or it may not go again, it's really early days.''
The weather for the rest of the day was ``not that good'' and there was still a lot of low clouds and drizzle around the mountains, he said.