Police and fire investigators are treating a fire at Queens House in Barnstaple this afternoon as arson.
Three fire engines - two from Barnstaple and one from South Molton - were called to the office block on Queens Street around 2.45pm today after the fire alarm sounded.
30 offices in the building were evacuated while officers searched the space between the roof and the ceiling on the top floor of the building.
Crew commander Wayne Keenan said: "We found evidence of two small fires in the loft space but both were out on arrival.
"Fire fighters made the scene safe and then allowed workers back into their offices.
"After carrying out an initial investigation we are treating this fire as arson and will be investigating the matter with the police."
Robert Vogler of Eclipse Financial Solutions, which is based on the first floor of Queens House, said: "When the alarm went off we assumed it was a drill but we evacuated anyway.
"You couldn't see any flames or smoke but apparently people on the top floor heard someone running around in the loft above them."