Detectives say three people were stabbed. Reports also say one gunshot was fired.
One victim is at Hahnemann Hospital in critical but stable condition.
Several people were taken into custody.
A man, who didn't want to be identified, was an eyewitness to the chaotic scene.
"They were basically just brawling in the middle of the street. Then a few ran that way, then a few ran this way, then they came back and started fighting once again," the witness told Action News.
Investigators believe the fight initially started at the Hispanic Festival at Penn's Landing and spilled into the streets outside the event.
This was the second unruly large crowd within the past 24 hours for police.
On Saturday night, a group of teens assaulted several people on South Street.
Hundreds of officers responded and the crowd broke up.
Three people were arrested.
Police are not calling these two incidents flash mobs as they do not appear to be orchestrated events.
