Assistant police Chief Daniel Warg tells The Morning Call of Allentown the chunk of building fell off the shuttered 13-story Americus Center on Saturday night.
Building owner Albert Abdouche says he's still trying to determine where the falling concrete broke off.
He told the newspaper last month a number of code issues had been fixed and the building was safer than ever when he successfully sought permission to remove scaffolding erected to protect cars and pedestrians.
The building has been unoccupied since 2002 when it was declared unfit for habitation.
Information from: The Morning Call