Crews were called around 8:45 p.m. Thursday to the 5000 block of Flat Rock Road.
Firefighters found flames shooting from the roof of the vacant building.
The building, once known as the Paperworks Philadelphia Mill, has been vacant since 2017.
Flames burn through large, vacant Manayunk building
No one was injured in the two-alarm fire.
Investigators are still trying to find how it started.
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