A major blaze at a former Wigan cultural landmark is being investigated as arson.
Firefighters were called to the vast site of Eckersley Mills just before 1.30pm on Sunday.
A gang of youths was spotted fleeing the scene shortly before, authorities have said.
Crews from Wigan, Hindley and Skelmersdale tackled the flames in an abandoned building for around three hours and were able to prevent it spreading further.
A fire service spokesman told Wigan Today: "There's no way it could have started without it being deliberate."
The fire is thought to have been started in a roof space with waste materials from the site set alight.
Eckersley Mills is the borough's largest collection of Victorian-style mill buildings, along with several offices, and has long been subject to grand planning applications to convert it into a cultural hub.
Three of its industrial units were destroyed in a fire in July 2012 and the latest blaze follows a similar pattern to that of another abandoned mill building at the Pagefield site, close to Mesnes Park, which has also been a regular scene of deliberate fires.
The fire spokesman added: "They've gained access to the site, because it's so vast it's not that secure, and used some waste materials to start the fire. It has spread into the roof but our officers have worked really hard to bring it under control.
"It's similar to Pagefield in that these fires are not only putting those who start them at risk but they're really difficult for our officers to tackle.
"Police officers attended and are treating it as arson, a caretaker for the site saw some kids running out (shortly before the fire was reported).
"Parts of the site are still occupied and (the fire) could have spread to them."
Crews left the scene shortly after 4.30pm.