Firefighters from across Lancashire are tackling a large fire at the former Accrington Conservative Club.
Fire crews and police were called to Cannon Street in the town centre at around 3.50am on Wednesday morning.
Nearby residents have been evacuated to the Tesco Extra store on nearby Eagle Street.
Lancashire Police said the cause of the fire is not yet known, however they have not ruled out an arson attack.
Gary Hargreaves, Hyndburn fire station manager, said they got the initial call at 3.45am.
He added: "We have eight fire engines and two aerial ladder platforms and a control unit. There is severe damage to the building which was previously used as a Conservative Club. Firefighting is still in progress.
"Crews will remain here throughout most of the day.
"There are road closures on Paradise Street and Cannon Street and they will be in place until a local building inspector assesses the stability of the building. The cause of the fire is still under investigation by ourselves and police. Arson isn't being ruled out but everything is being considered at this time."
The building is currently derelict and has been subjected to numerous fires in recent years.
Former firefighter Elliott Anderson, from Accrington, said: "It's a real shame as it is a great architectural building. The whole roof has collapsed through the top floor and the wood and rafters on other floors have been damaged. It will probably have to be demolished, which is a great shame."