Police made a show of force in Center City yesterday after they were alerted that large groups of teens planned to gather in response to two fights at the Gallery at Market East.

Security guards were posted at every entrance to the Gallery and did not permit juveniles without adults to enter, said police spokesman Lt. Frank Vanore.

Throughout the afternoon, police monitored gangs of youths - some numbering up to 100 - as they roved from the Gallery to other Center City locations.

Officers followed the teens on Market, Chestnut and Sansom Streets from Ninth to 16th Streets.

Despite the elevated police presence, some bystanders said they were assaulted.

Jane Lessner, a Center City lawyer, said she had just left Macy's after doing some holiday shopping when she saw a group of 70 to 100 youths near Broad and Chestnut.

Lessner tried to make her way through the group when "they started pushing me."

"One pushed me into another, who pushed me into another, who pushed me into another until one girl hauled off with her fist and hit me in the face," Lessner said.

The punch knocked a lens out of her sunglasses and left her with a bloodshot eye.

Brendan Meehan, 44, of Media, who also was Christmas shopping, saw the attack and called for help.

"I saw a teenage girl hit her right in the face," he said. "The girl came back and taunted her as I called 911."

Police Lt. Michael Brady said there were fights Wednesday and Thursday at the Gallery's food court that resulted in four arrests.

Calls for a massive gathering then surfaced on Facebook, he said.

He said students from at least three high schools were involved.

"They're from other sides of the city. We don't know why they're doing it, but they're gathering here," he said. "They're trying to create some sort of disruption."

A spokeswoman for the company that owns the Gallery said mall officials met before lunchtime with city and School District police.

"The Gallery is working with the City of Philadelphia police to significantly increase security coverage of the Gallery in response to roving groups of disruptive teens in Center City," said Judy Trias, spokeswoman for Pennsylvania Real Estate Investment Trust, with headquarters in Philadelphia.

"We believe the increased presence of law-enforcement and security personnel will deter any bad behavior and protect the safety of our shoppers and merchants," Trias added.

Fernando Gallard, a spokesman for the Philadelphia School District, said officials there heard from city police "regarding possible altercations involving students in Center City, specifically at the Gallery."

Gallard said police informed them the students came from Audenreid and South Philadelphia High Schools and from Preparatory Charter School of Math, Science, Technology and Careers, which is in Point Breeze.

Gallard said the district was working closely with Philadelphia police and had dispatched extra school police to the involved schools.

"We had a very smooth closing in our schools," Gallard said.