Emergency services were called to an incident on Bridge Street in Church, close to the roundabout with Blackburn Road and Henry Street, at around 2.30pm today (March 25).
When firefighters and paramedics arrived at the scene, an injured man was found "conscious and breathing".
It is believed the man was working on the roof of a derelict building before it collapsed.
He was taken to hospital for treatment.
A spokesperson for Lancashire Fire and Rescue Service said: "Firefighters from Hyndburn, Great Harwood along with the aerial ladder platform from Hyndburn and Urban Search and Rescue team from Chorley were called to an address on Blackburn Road, Church, Accrington after receiving reports that a man had fallen through a roof.
"Firefighters worked alongside paramedics offering first aid to the casualty before rescuing the casualty from the building.
"The casualty was then taken to hospital via ambulance. Firefighters were in attendance approximately one hour and forty minutes."
North West Ambulance Service reportedly sent two rapid response vehicles, an ambulance and an air ambulance at 2.31pm.
The nature of the mans injuries is not yet known.