"We're trying to charge them with the highest charges we can bring," he said. "The message is, don't come back to this area if you're going to cause trouble."
The District Attorney's Office expects to decide on charges for the youths by early today, a spokeswoman said.
James B. Golden Jr., the School District's chief safety executive, said most of the students were from city schools, but authorities still were sorting out which ones.
Vanore said officers made 18 arrests, but police at Central Detectives, which is handling the investigation, said later that 28 juveniles had been taken into custody.
Unlike the incident in February, when a wave of teenagers rushed through Macy's and vandalized the store, yesterday's melee appeared to cause no property damage.
In previous incidents, teenagers assaulted pedestrians and pulled people from their vehicles. Yesterday, a Highway Patrol officer was elbowed in the mouth, but otherwise there were no injuries, police said. One student was expected to face an aggravated-assault charge for hitting the officer.
Some officials have complained that the incidents, which began in May along South Street and sprang up again this winter around the Gallery, are tarnishing the city's image.
Some of yesterday's arrests occurred several blocks from the Convention Center, where the Philadelphia International Flower Show is under way.
Everett Gillison, the deputy mayor for public safety, said "these are isolated incidents" that will "peter out."
"There's no growing wave of violence," he said. "If people come for the flower show, they'll be safe. There is no problem there."
Witnesses to yesterday's trouble said a group of teenagers chased a man, who appeared to be older, down 15th Street. The man ran into a CVS store at 15th and Chestnut with the teenagers in pursuit.
