Firefighters tackled a blaze which badly damaged a disused former Chorley steel merchants.
Less than a fortnight ago, a warning was issued after arsonists struck at the same premises.
This latest blaze at the former Bonney Greenhalgh & Co Ltd property on Back Ashby Street, not far from the town centre, is being treated as suspicious by fire chiefs.
Fire crews, including one from the Greater Manchester area, rushed to the incident after receiving the emergency call on Tuesday afternoon.
The alarm was raised by nearby resident Doug McBurney, 41, of Duke Street, whose house backs onto the building, which is close to a timber yard and pub.
He said: “I’ve got the back window open and was listening to some music. I could hear some banging noises, then it sounded like popping noises. I went to the back and saw the entire back half of the building was on fire.”
Mr McBurney, who works as a security guard, said he understood a building firm has been dismantling the premises.
“If they hadn’t taken the roof down, all the back houses here could have been at risk. That fire could have been right up against their walls,” he said. “It had me shocked, so it did.”
He added: “I saw people who I suspect could have done it.
“A group of teenagers went past about five or ten minutes before. There were about six, aged about fifteen and seventeen.”
Another resident, Elaine Heath, 66, of Back Ashby Street, opposite the building, said: “I heard crackling noises and looked out of the window.
“The first thing that came into my head was my car’s parked here.
“I came out and saw all the flames.
“It’s been derelict for quite a while. They’re moving things out.”
Jean Gootell, of Duke Street, said: “I just saw black smoke coming out.
“It’s been derelict for a while. There’s a man called taking it down, but I don’t know what’s going to happen.”
The emergency call was received at 2.19pm.
The fire involved a derelict building about 20m x 10m, consisting of two floors. The ground floor was well alight.
Firefighters used four breathing apparatus and three hose reels.
John Taylor, senior communications officer for Lancashire Fire and Rescue Service, said: “It looks suspicious. We are still investigating.”
Last month, firefighters quickly attended the eyesore site after firebugs had struck. There was no immediate damage.
The building is currently up for sale and has been on the market for one year.
After that attack, councillor Bev Murray, ward councillor for the area, said: “Disused buildings can be a target but it’s very difficult to do something when it is privately owned.
“The council do have powers to ensure the safety of buildings like this.
“I know of other buildings that have been targeted including the Asda site when the QS Fashion building was still there.
“It is definitely an issue which needs highlighting and something needs to be done in the future.”
Anyone with any information on the fire can contact police on 101.