Horsham District Council has evacuated its offices after a report of smoke in the first floor this afternoon (Friday January 31).
Firefighters were called to Park North in North Street at around 3pm.
Two units from West Sussex Fire and Rescue Service attended.
Council staff evacuated the building and sought refuge in the neighbouring Capitol Theatre.
A spokesperson said firefighters responded to a report of smoke issuing in the first floor which appeared to be coming from a light fitting.
Thermal imaging cameras are being used to investigate.