The factory on Port Road in Kwinana broke out at around 1.30pm AWST (4.30pm AEDT).
The smoke is affecting Kwinana Beach, Medina, Orelia, Parmelia, Bertram, Wellard, Leda, the Kwinana Town Centre Kwinana and Rockingham.
The affected areas have been issued hazmat warnings, with residents advised to remain inside with doors and windows shut.
Firefighters are on the scene.
