A gunman who opened fire inside a Pennsylvania shopping mall remained on the loose Sunday morning, hours after dozens of police vehicles surrounded the building and officers rushed in to evacuate frightened shoppers.

The shooting happened at Lehigh Valley Mall in Fullerton, Pa., shortly before 5 p.m. Saturday.  No injuries were reported.

Four shots were fired in the lower level near a sporting goods store, Whitehall Township Police Chief Michael Marks said.

"The responding officers needed to get into the mall and make sure there was no active gunfire occurring at the moment," Marks said Saturday night, according to WFMZ. "As far as our secondary operations right now, that's just making sure that the mall is empty and we were able to account for everybody employed or at least at the mall at that point."

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Shoppers recounted a chaotic scene, as the shots rang out and panicked people streamed out of the mall, followed quickly by officers racing in.

Those remaining inside were instructed to shelter in place while police went store to store evacuating people and looking for potential suspects and victims.

“I will never forget the second of silence that happened after the shots, as we processed what we heard,” said Ashley Giammona, who was shopping on the second floor with her husband. “Then everyone started screaming. My husband slid behind a jewelry display in the middle of the mall, and I army-crawled to him."

About three dozen police vehicles, including an armored truck, and four ambulances responded to the shooting. The Whitehall and Allentown police departments, and Pennsylvania State Police troopers, were on the scene, The Morning Call reported.

No arrests have been made as of Sunday, and no motive behind the shooting was released.  Investigators were reviewing surveillance footage in hopes of identifying a suspect.

Authorities called for anyone in the mall at the time of the shooting who may have cell phone video of the incident to contact police.

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Lehigh Valley Hospital and St. Luke’s University Hospital were put on alert in case anyone injured left the mall undetected before law enforcement arrived, The Morning Call reported.

Allentown Police Capt. Mike Becker told The Associated Press that his department was assisting Whitehall Township Police but had no other information to share.

Cheryl Furler, an employee at Bath & Body Works, told WFMZ that she and about 50 other people barricaded themselves in the stockroom.

“We took filing cabinets and pushed them up against the doors," she said.

“Kids were really upset," recalled Lucy Usoyan, another shopper. "That’s what makes me really upset."

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Ronny Garcia said he sheltered in the back of a store with other customers for a half-hour.  Police evacuated them before most mall patrons when a woman began to go into labor, he said.

The Associated Press contributed to this report.