Auckland's St Kentigern College has revealed what led to a blaze in one of its classroom buildings this afternoon

Fire crews were called to the Pakuranga school at about 1.30 - after huge plumes of smoke were spotted.

The school says a spark from tools being used in its technology building landed on wood shavings - causing smoke to move through the building.

It says all staff and students are safe, and were allowed back in the school by around 2pm.

Fire and Emergency's confirmed it wasn't a major blaze - and there was no risk to other buildings.