An estimated 500 youths swarmed through Dilworth Plaza in front of Philadelphia City Hall Wednesday afternoon as police tried to control angry flare-ups between teenagers.

“It was the perfect storm,” said one police source. “It was the worst it has ever been.”

The source credited the warm weather and social media with bringing a massive number of youths to the area.

City and SEPTA police, who have deployed contingents to the areas around City Hall and Dilworth Park SEPTA stations in recent months to quell frequent after-school violence amongst youths, were both on the scene.

"The youth of our city are off the hook in Center City," SEPTA police chief Thomas Nestel III tweeted just before 4 p.m. Wednesday. "Weather has brought large number of students to Center City. While many are enjoying day, some are out of control."

Massive crowds filling the sidewalk on Market Street were seen around 3:30 p.m., while at least two young people were cuffed and led into a police wagon.

By 4:30 p.m., Dilworth Park was shut down, and authorities had warned store owners on Chestnut Street to close their doors because “we couldn’t guarantee their safety,” said one officer.

Bicycle cops and other officers quickly evacuated the plaza amid reports of fights and ordered youths to disperse.

An increased police presence remained around City Hall Wednesday evening.

Dilworth Park was reopened to the public, but youths in the park were still being told to leave.

Witnesses to the fight declined to be identified, but one commented that youth violence outside the City Hall station is common.

"It happens every day," one said.

Police officials declined to comment on the record on whether their presence in the area would be stepped up in the days to come, but some implored parents to help address after-school violence in Center City.

"We're urging parents of students to help us out, even if their child isn't someone who would be involved in any type of disturbance, it would help greatly if they would check and make sure their kids come home right after school," said SEPTA spokesman Andrew Busch. "They can be innocent victims standing around when something happens. We want to see that limited as much as possible."