Authorities say about 100 firefighters battled the blaze at the Penn Glass Inc. plant just south of Lancaster.
The fire was reported about 11:30 p.m. Saturday and took until 4 a.m. Sunday to control.
Nobody was found inside the building and authorities wouldn't confirm a report that a door to the factory had been broken. The family-owned business closed last fall and the building had been for sale since December.
Authorities initially heard screams coming from the area, but later determined they didn't come from inside the building but from hundreds of bystanders watching the blaze outside a nearby bar.
