Two youths were believed to be missing inside a burning building when it was set alight.
Firefighters were called to a disused property on Sidings Road, Fleetwood, at 7pm last night when thick black smoke could be seen pouring out of the derelict former fish curing factory.
The blaze, which is being treated as suspicious and is under investigation by police, broke out when rubbish and tyres were ignited.
Three crews - one each from Fleetwood, Forest Gate and Bispham - were called to tackle the fire, and conducted a search of the building when they arrived after being told youths were missing.
However, the two missing youngsters turned up elsewhere minutes later.
Crew manager Kevin Warwick from Fleetwood Fire Station, said the building has been regularly targeted by arsonists over the last six months.
He said: “This could have been avoided.
“It was a waste of resources, and the amount of resources it took to tackle the fire and search the building was unacceptable.
“If kids are going to play in there someone is going to get hurt.
“We’ve had issues in there before with smaller fires, but this was a big one and we couldn’t be sure of the danger until we looked at it.”