Fire crews have worked through the night to contain multiple fires within a commercial building in Mayfield.
Fire and Rescue NSW crews were called to Frith Street just after midnight.
On arrival, they found a hydraulic line from machinery had burst, causing it to ignite.
This created multiple fires in the building that spread to the control room of the factory.
More than 40 firefighters battled the blaze for a number of hours before containing it just before 4am, however, the building suffered severe damage.
About 40 people were evacuated from the area, with one treated by NSW Ambulance paramedics for smoke inhalation.