PHILADELPHIA (CBS) – Another flash mob attack in Center City left two men beaten so severely they had to be rushed to a local hospital. Shocked onlookers called 911 leading to several arrests, and Eyewitness News’ Elizabeth Hur reports that one of those suspects is just 11-years-old.

Witnesses, who asked to remain anonymous for their safety, could hardly believe it.

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“It looked like a bunch of roaches just swarming,” one witness said.

“You see 40 or 50 kids and they’re up to no good,” another said.

According to police, it happened just after 9 p.m. Friday at Walnut and Juniper Streets. Police said a mob of teens surrounded a 53-year-old man and beat him.

“His whole face was bloody,” one of the witnesses said. “He wasn’t conscious by the time police got here.”

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Police said the same mob then attacked another victim near 15th and Sansom Streets. A 33-year-old man was beaten and then robbed of his wallet and cell phone in that incident, investigators said.

“It was real bad. The guy got up, staggering, falling back down,” a witness said.

This is just the latest in the wave of flash mob attacks in Philadelphia, and most recently, Upper Darby. Flash mobs by definition means a group of people assembling suddenly. They’re typically a peaceful gathering, but no so in Philly, leaving residents nervous.

“The past couple months, sometimes during the weekdays, cops on Chestnut Street are really trying to prevent this type of thing from happening, but I guess there’s only so much you can do,” a concerned resident said.

Police said they are doing their best, monitoring Facebook and Twitter activity to try and stay ahead of the pack.

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Four individuals were arrested from Friday night’s attacks, including an 11-year-old for conspiracy and assault-related charges.