Story highlights State police say a possible suspect has been identified

Mayor: Authorities believe the gunman has left the mall

A store-by-store sweep of Westfield Garden State Plaza is ongoing

There are no immediate reports of injuries

A shooter opened fire at a New Jersey mall late Monday, sending panic through the shopping center and igniting a massive police response.

The gunman inside Westfield Garden State Plaza Mall in Paramus, New Jersey, had not yet been found during a sweep of the shopping center by Bergen County SWAT, said county Chief of Staff Jeanne Baratta.

But authorities have identified a possible suspect, New Jersey State Police Sgt. Joe Lettieri said.

Authorities swept through the mall store-by-store late into the night. Mayor Rich LaBarbiera said there have been no injuries, and authorities believe the gunman is no longer in the mall.

At least one gunman is said to have fired shots at security cameras, the state police said.

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A single shell casing has been found, a Bergen County emergency management official said.

Eddie Kahmann, who works inside the mall, told CNN he heard 6 or 7 gunshots around 9:20 p.m. ET.

"There was just people running like crazy, so I quickly just closed my doors, ran to the back, turned off all the lights, music and everything, just to stay hidden," he said.

Kahmann spoke from inside the mall, one of the largest shopping centers in the New York City area.

Allie Cozic, another mall employee, said she saw "someone dressed in all black, carrying a large gun, walk past our store."

She said she heard loud bangs about 10 minutes before her store was set to close for the night.

"It was just chaos. Everyone was just kind of running to wherever they could," Cozic said.

"It was almost like when you're watching a horror movie and the killer is walking slowly -- that's what it seemed like. He was wearing all black, it almost looked like body armor of some kind. As soon as I saw the gun, I just turned and ran," she said.

There is a large police presence at the mall, which was set to close at 9:30 p.m. ET. There are about 20 vehicles both marked and unmarked.

The FBI, including an FBI SWAT team, was also on the scene. "There is a massive response from several agencies," according to a law enforcement source with knowledge of the investigation.

Police were putting on flak jackets and bringing out assault weapons. People were pushed away from the mall and were telling CNN that they've been told the shopping center was on lockdown.

Westfield Garden State Plaza is located some 12 miles from Manhattan. It boasts of being home to nearly 300 specialty shops and boutiques.