A gang of youths spotted close to a derelict hotel moments before it went up in flames are today being hunted by detectives.
Firefighters battled flames for almost four hours while facing life-threatening hazards in the abandoned three-storey Misterton Hotel, on Blundell Street, South Shore.
The fire is being treated as arson.
Nearby residents have described seeing groups of teenagers smashing windows at the property in broad daylight in the days leading up to the blaze.
Det Sgt Kathryn Riley, from Blackpool CID, is leading the investigation and is now calling on anyone with information about the arsonists to come forward.
She said: “It would appear a group of youths were seen in the area at the relevant time.
“We’re talking quite a decent number of youths.
“We are definitely seeking more witnesses.
“If anybody heard anything in the local area, do contact us.”
The gang is described as being around the age of 14, and more than five in number.
Det Sgt Riley added the investigation is “ongoing, but progressing”.
More than 30 firefighters from five different Fylde coast stations worked to put out the flames after the alarm was raised at around 7pm on Saturday.
They encountered missing floorboards and cluttered debris while they fought their way through the smoke-filled building, which has been abandoned for almost two years.
The building had ceased trading as a hotel in November 2012 and was compulsory purchased by Blackpool Council, along with most other properties on the street, with a view to it being demolished and rebuilt as part of the new Foxhall Village housing development.
Station manager Sean Hennessy, from Blackpool fire station, said: “The fire is still under investigation and the police are making lines of inquiry.”
Witnesses should call 101.