It began around 11:00 a.m. in the 5200 block of Westminster Avenue in West Philadelphia when police were called out tor a report of a man with a weapon.
Arriving officers said they were confronted by a man with a knife and they called for assistance.
What happened next is not clear, but two police officers discharged their weapons.
The man was shot multiple times and transported to the Hospital of the University of Pennsylvania.
Medics said his vital signs were "unstable."
Police say Internal Affairs will now take over the investigation.
The man shot by police has not yet been identified.