The power cut meant Ruahine School's water pump wouldn't work so the toilets were unable to be flushed. It also meant there was no drinking water for the children.
Parents were told to pick up their children as soon as possible, with the school posting the news on its Facebook page.
School board chairperson Lisa Charmley said power to the school was lost at around 8.40am.
The decision to close the school and send the children home was made at 8.50am.
All three buses that service the school were cancelled because of the force of the wind.
The school is nestled near the Ruahine Ranges, 12km southwest of Dannevirke. It has about 155 students.