A firefighter has been taken to hospital for "precautionary reasons only", following a large blaze at a Hokitika high school, a spokesman said.
Police are warning the public to stay away from the immediate area as the smoke is toxic.
Tasman District Acting Senior Sergeant Malcolm York said people needed to move away from the site as large plumes of smoke are said to be toxic.
A firefighter has already been taken to hospital, for what was said to be "precautionary reasons", a Fire Service spokesman said.
Mr York could not reveal any other details about what may be burning inside the two-storey administration block. The roof of the school's hall is also ablaze.