A Roosevelt Field mall worker was shot by an armed robber during a botched heist of an upscale watch store Tuesday afternoon, causing pandemonium in the crowded shopping mall just days before Christmas.

The single shot was fired as the robber, who was arrested at the scene, wrestled over his gun with a security guard at the luxury Tourneau watch store, authorities said.

The injured mall worker, a 67-year-old man, was shot by the stray bullet in the shoulder and hospitalized in serious but stable condition, authorities said.

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Shoppers described chaos inside the mall at the sound of gunfire, with throngs of people screaming and running, as a public already on edge after attacks in Paris and California feared terrorism or a mass shooting.

“People were just running; it was chaos,” said Ava Doshi, a Macy’s employee who heard the gunshot. “I was just scared. I just wanted to get out.”

Acting Nassau Police Commissioner Thomas Krumpter said, “The motive was clearly a robbery. This was not an active shooter.”

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Nassau County Executive Edward Mangano said the suspect entered the Rolex area of the Tourneau store about 1 p.m. and made his way to an area with a particularly high-end selection. As he tried to leave, the robber struggled with a store security guard, who Mangano said “acted swiftly,” and his handgun went off, striking the employee who was outside the store, officials said. Police recovered the weapon but provided no description.

“Our thoughts and prayers are with the innocent mall employee that was shot,” Mangano said, declining to say where in the mall he worked.

Police are investigating whether any other suspects were involved. Neither the shooter nor the victim was identified by police. A police spokesman said the suspect’s name and charges will be released at a news conference Wednesday.

NYPD Insp. Kenneth Lehr, commander of the fugitive enforcement division, said he was at the mall Christmas shopping and saw a stampede of people running, so he ducked into the vestibule of a store and waited for the crowd to clear.

“I thought for sure it was going to be an active shooter situation,” Lehr, 49, said, and as the corridor cleared he saw a struggle about 20 to 30 yards away. “It was a wrestling match, basically, for the firearm.”

Two uniformed Roosevelt Field security guards and a man in a suit — a retired NYPD officer who works as a security guard in the watch store — struggled with the suspect, Lehr said. Handcuffs dropped to the floor, Lehr said, and he picked up the cuffs and helped secure the suspect.

“I don’t want to make this sound like I did anything alone,” Lehr said. “The heroism was on the part of that security person, the retired detective, what he did was remarkable; the two security guards, they are not armed, they raced into that store, they were there before me. I simply helped them close the deal.”

Lehr said he did not remove his firearm from its holster.

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Krumpter said he could not immediately confirm Lehr’s account.

Alexandra Santini, 33, of East Meadow was working at a seasonal shop near Tourneau and said she witnessed a fierce struggle between the shooter and security guard.

“The guy that works at Rolex, he was in a suit . . . he was holding some man [the shooter],” said Santini, who was later seen talking to a detective. “I saw him dragging him.”

After the shooting, the Garden City mall remained open, though the crime scene in the Neiman Marcus wing was closed to the public, Mangano said.

One person was shot and another was arrested after a shooting Tuesday, Dec. 22, 2015 at the Roosevelt Field mall, a police official said. The shooting left some shoppers scrambling to get to safety, in full panic mode, one of those shoppers told News 12 Long Island. Photo Credit: Twitter / Michael Nex

A spokesman for the mall, owned and operated by Simon Property Group, declined to comment. The mall has been undergoing a $200 million expansion and renovation.

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The three-level mall, which opened in 1956, is the largest enclosed mall on Long Island, sprawling over 2 million square feet with more than 270 stores.

A Tourneau company spokesman could not be reached for comment and no one answered the phone at the Tourneau store, which was the site of a September 2014 smash-and-grab robbery that netted three thieves $230,000 in high-end timepieces. Krumpter said Tuesday’s botched robbery was not connected to the previous heist.

Krumpter described the police detail assigned to the mall as “significant and very robust.” He recently told Newsday he had added a supervisor to the detail.

“After Paris, we heightened our response to these soft targets and heightened the number of patrols,” Krumpter said. “And we maintain that at this time.”

With Anthony M. DeStefano, Aisha Al-Muslim, Laura Blasey, Chau Lam and Ellen Yan