Six fire engines from Burnley, Nelson, Bacup, Rawtenstall, and Colne, as well as an aerial ladder platform from Hyndburn and the air support unit, were called to the premises in Talbot Street at 5-45pm.
Ormerod Road has been shut by police as firefighters continue to bring the fire under control using five jets.
Residents are being asked to keep their windows and doors closed to avoid any smoke.