The fire took hold at the old Polestar Petty premises on Whitehall Road at about 12.45pm today.
Thick clouds of smoke could be seen billowing from the roof of the building.
A section of the roof was also well alight and a number of loud bangs were heard.
The worst of the blaze appeared to be over by around 2pm although half-an-hour later firefighters were continuing to hose the building’s roof with the help of two aerial ladders.
The section of Whitehall Road nearest the site was closed to traffic.
The factory shut at the end of 2014, nearly 150 years after Petty & Sons first began operating in Whitehall Road.