Fears of an explosion at a block of flats in Leamington Spa led to a 999 call and a major fire crew response.
Warwickshire Fire & Rescue service were called Dale Street at about 1030 BST and deployed crews with breathing apparatus.
On investigation it was discovered the incident was caused by a collapsed ceiling on the fourth floor. No one was hurt.
Group manager Greg Pace said: "The dust had given the impression of smoke."