Police vehicles from multiple municipalities lined the Bond Shopping Center at Lansdowne and State Road in Delaware County.
Upper Darby Police say officers were working to help people clear the area when "numerous" people refused repeated instructions to leave and began disrupting local businesses and others who were going home.
Roughly 15 people have been arrested, according to police, and more are expected.
Officials said those arrested are a mix of juveniles and adults.
Upper Darby police report numerous arrests after disturbance following community fireworks
Police say they were monitoring social media before and during the event and this came up as the event was going on.
Authorities say officers gave multiple warnings before making arrests.
A woman was live-streaming the crowds of people and the responding officers trying to disperse them when you hear what sounded like gunshots.
Action News has confirmed that that it was not gunshots, but fireworks.
Due to the size of the crowd, Upper Darby police asked for assistance from other municipalities. Pennsylvania State Police troopers were among those who responded.
RELATED: Looking for fireworks near you in the Philadelphia area? Check out this list
Both neighbors and police say this never should have happened.
"Parental guidance, of course, that definitely needs to do better and improve, but that's just sad to hear things like that going on around here," said Robert Hinton of West Philadelphia.
"They want us to find activities for their kids and here was a perfect opportunity. A perfect activity. There was everything there last night for everyone in this community and outside this community to enjoy, and unfortunately they came and they ruined it," said Upper Darby Police Superintendent Timothy Bernhardt.
In New Jersey, two communities cancelled festivities due to security concerns.
In Mount Holly, public safety officials say there have been too many large events lately that have gotten out of control.
In addition, Gloucester Township Day -- a summer celebration typically held in June -- was cancelled for the second year in a row after large groups of juveniles got out of control.