An investigation is under way after a blaze at a factory in the West Auckland suburb of Avondale on Saturday afternoon.
The Fire Service received calls just before 5pm reporting large amounts of black smoke coming from the factory on Honan Place.
The fire had broken out in an acid bath at the rear of commercial units.
About 50 firefighters and two hazardous material teams were called to the scene, and the firefighters needed to be decontaminated.
The fire took four hours to put out.