Emergency services were called to the Star Combo Pharma premises in Smithfield at 2pm after reports of large volumes of smoke coming from the building.
Firefighters and a major incident management team were still at the scene tonight as the fire burned out.
No one was inside when it took hold, but residents of nearby Greystanes were warned to stay indoors and avoid the area due to fears of smoke inhalation.
Local roads were closed.
The company manufactures pharmaceuticals, cosmetics, vitamins and nutritional supplements, shipping nationwide and worldwide.
It is believed to have just completed a multimillion-dollar factory upgrade to meet global demand.