Six fire engines from Clitheroe, Great Harwood, Hyndburn and Blackburn, the command support unit, the aerial ladder platform from Hyndburn and the stinger from Blackburn, were mobilised to an incident on Waddington Road in West Bradford.
On arrival, crews found the commercial building to be well alight.
Six firefighters wearing breathing apparatus are currently using three hose reels and two jets to extinguish the fire.
Crews remain at the scene.
UPDATE AT 08:35:00
Firefighters were at the scene for over 18 hours damping down hotspots in the roof of an annexe building. A fire investigation is now underway. No injuries were reported.