While the area had been put on alert for earthquakes the eruption still came as a very major surprise as it loudly rumbled into life at 11.50pm last night. It sent ash and rock a kilometre into the air, and surprised residents and trampers by the volume of the noise as well as the eruption itself.
While flights had been suspended throughout the day they have now been resumed, but the area remains covered in ash.
Niwa principal scientist Michael Uddstrom said the cloud from the event was 25km long and 15km wide.
"The temperature at the top of the cloud (associated with the eruption) is minus 54 degrees centigrade and it's about 12km high at its highest point in the atmosphere."
"We know from looking at sediment cores from Auckland lakes that ash from Tongariro has reached Auckland many times over the last 80,000 years. Of course it only needs to be in the atmosphere to cause a problem," University of Auckland vulcanologist Dr Jan Lindsay said.
GNS scientist Brad Scott said there was strong seismic activity for about 15 to 20 minutes after the eruption , however in the 24 hours prior and hours since, there had not been any significant activity.
About two dozen sceintists are in the area trying to ascertain the cause of the eruption,
.Last picture Hawkes Bay Today