Mt Tongariro erupted around 11:50pm on Monday, spewing ash and throwing rocks up to 1km from the mountain.
The eruption surprised geologists, who described it as “unexpected”, and it prompted a threat warning for the central North Island.
An eyewitness says the sky lit up with “flames and sparks”.
The mountain continues to be closely monitored by scientists and Civil Defence.
Watch the video to view aerial footage of Mt Tongariro.