A transient was arrested in Portland early Friday morning after firing four shots from a high-powered pellet gun at an unarmed security guard at One City Center, police said.

Ajay Narayanan, 36, was arrested by police after the security guard chased him down Congress Street.

No one was injured, but the pellets left quarter-sized holes in the doors of One City Center, which overlooks Monument Square.

Mike Conicelli, the overnight security guard, noticed Narayanan standing outside the Monument Square entrance shortly after 5 a.m. The man was slumped over and Conicelli approached him to see if he needed help,

“He was agitated right off the bat,” Conicelli said. “I first asked how he was doing, then asked him to move on.”

Conicelli said Narayanan – whom he had never seen before – began swearing at him as they stood near the building. He then lunged at Conicelli, who punched him in the face.

“He swore at me again, then stepped back and pulled out his gun,” Conicelli said. “He said, ‘You’re not a big man now’ and fired four shots on either side of my head.”

Conicelli said he thought it sounded like a cap gun instead of a real one, so he gave chase as Narayanan took off running toward the Congress Street entrance of Portland High School. While on the phone with a 911 dispatcher, Conicelli chased the man down Congress Street to the Portland Public Library.

“She (the dispatcher) told me to stop pursuing him, but I thought the gun was fake,” said Conicelli. “When I got back to the building and saw the holes (in the doors), I couldn’t believe it. I didn’t realize it was real. I could have been dead.”

Narayanan was arrested by Portland police near 205 Oxford St., according to Lt. James Sweatt, and taken to the Cumberland County Jail.

He was charged with criminal mischief, criminal threatening and reckless conduct with a dangerous weapon. Police said they have had previous dealings with Narayanan but could not provide his criminal record.

Shortly after the arrest, officers searched for the pellet gun, but Sweatt said later in the day that he didn’t know if it had been found.

Dale Knight, client contact liaison for One City Center Security, found three pellets outside the building two hours after the shooting.

Maine law restricts sales of pellet guns to people under the age of 16, but no background check is required to purchase one. Pellet guns use compressed air or gas to propel pellets, compared to firearms, which use a propellant charge.

By late morning Friday, building maintenance had covered the cracked glass with duct tape.

Jim O’Donnell, president of Dirigo Management, the company that manages the building, said Friday’s incident underscores the importance of improving security measures at the building, which houses a number of businesses, including the law firm Preti Flaherty and the Portland Press Herald.

O’Donnell said money already has been budgeted to install new cameras next year, both at the 12-story office building and in the One City Center parking garage, which has been hit by a rash of car break-ins over the last several months.

In June, the Bank of America branch inside One City Center was robbed by a man who fled on foot. That crime is still under investigation and police have not yet found the robber.

Conicelli, the security guard, said a police officer told him that the shots from the pellet gun would have been strong enough to kill him if he had been hit. He said police also told him Narayanan was carrying a second full magazine.

Conicelli has worked as a security guard at the building for 13 years. He said the shooting was the first incident of its kind he’s been involved with at the building.

“It was unprovoked and very odd,” Conicelli said. “I did not see it coming. It was a split-second thing.”

Staff Writer Eric Russell contributed to this story.