The girls were arrested, along with 12 others, Dorsey said.
"We don't know at this point if they were here to watch a fight or a fight spontaneously broke out," Dorsey said.
"At some point, bottles were thrown at police," but no one was hurt, Dorsey said.
The Wendy's restaurant on the northwest corner of 15th and Chestnut, a popular hangout for teens, was closed because of the ruckus.
Three females and 11 males were arrested and Dorsey said she believed they were all juveniles.
She said she did not know which schools they attended.
Officers from several departments responded to the incident, including city police, School District officers, SEPTA police, and the Sheriff's Department.
Dozens of officers from many departments were dispatched because the area is a transportation hub, Dorsey said.
At 4:45 p.m., officers on bicycles were still blocking off sidewalks at 15th and Chestnut. Most of the teens had scattered.
"We're just trying to straighten things out until things are normal and calm," Dorsey said. "We don't know why it happened. It just happened."