Updated

A pack of 30 teens helped themselves to items in a Maryland 7-Eleven early Sunday morning in what authorities have labeled another instance of a possible flash mob.

The store, which is located in Germantown, Md., was empty at 2 a.m. Sunday morning when a group of teenagers calmly walked in and picked out items as though they were shopping. Then, just as calmly as they entered the store, police say, they exited without paying for the items.

A surveillance video from the store obtained by FoxNews.com shows a large group of teens taking candy and other snacks. They appear quiet during the incident and some appear to cover their faces with their shirts in an apparent attempt to avoid identification.

“As criminals go, they were pretty neat,” Howard Hersh, a spokesman from the Montgomery County police. “There were no injuries and they didn’t ransack the store.”

He said police are investigating the matter, and have extensive resources in place to track social media in the community that may organize such mob scenes. This is the first instance where a possible flash mob took to a store in the county. No arrests have been made.

Prior to Sunday’s incident, community leaders called for a mandatory curfew for teenagers in the area when groups started to appear on street corners.

Police departments in several U.S. cities are investigating what appear to be incidents of "flash mob"-generated violence, in which packs of dozens or even hundreds of youths appear seemingly out of nowhere to commit assaults, robberies and other crimes against innocent bystanders, according to an earlier FoxNews.com report.

Philadelphia Mayor Michael Nutter, who recently imposed a stricter curfew in response to the city's latest attack, addressed black youths directly from the pulpit of his church on Sunday, reportedly saying, “You have damaged your own race.”

The group in Germantown also appears to be predominantly black.

Similar attacks are also being investigated in cities like Los Angeles, Chicago, Cleveland, Washington, D.C., and Milwaukee.