A hero bystander who helped restrain a man at Sydney Airport on Wednesday said it was a miracle that nobody was hurt after a gun discharged in the terminal.

William Wilcher, who is a Sydney barrister and former NSW Police dog handler, and his off-duty police officer friend rushed to help AFP officers to restrain the 41-year-old man.

He was arrested near gate 49, metres away from popular venues Veloce cafe, Wine Selectors, and Fat Yak Bar.

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An AFP officer’s firearm unintentionally discharged just after 6am yesterday.

Earlier reports suggested the arrested man attempted to grab the AFP officer’s gun. However, authorities are still investigating the incident.

Wilcher shared what he saw with Sunrise host Nat Barr on Thursday.

“As we were going towards the gate, there was a disturbance, with AFP officers who were struggling with a man,” he said.

“It was a struggle that went to ground.

“The sergeant and I assisted and it was a team effort in bringing the person down and getting him safe.

“Unfortunately, the firearm discharged on the ground.”

When asked by Barr about the firearm discharge, Wilcher said, “I couldn’t see it discharge because it was underneath the fellow and his right arm was also underneath him with the firearm.

“I took control of his left hand and applied a very strenuous wrist lock on him to try to get compliance from the right hand.

“(My NSW Police officer friend) was going to take control of the right hand.

“He would be handcuffed.

“The fear was if he got loose with that firearm in the airport, there would have been a much bigger story.”

Barr asked: “Who had the gun?”

Wilcher said the rifle was on the floor.

“It somehow found its way on the floor.

“The man was over the top of it. He was lying upon it.

“His right arm was underneath the body in the vicinity of the firearm.

“I had control of his left hand. I was applying a very strenuous wrist lock.”

Sunrise co-host Matt Shirvington asked Wilcher if he believed someone had been hit in the terminal.

“You don’t think about it when it happens,” Wilcher responded.

“You just deal with what you’ve got. It actually probably made me apply more force to the wristlock to get more compliance of the right arm.”

Wilcher described the offender as “very agitated” person.

“I’m not sure if there was overstimulation by amphetamines or some mental health illness or something operating with him, but he wasn’t the normal garden variety hoodlum you might expect causing trouble at the airport.”

Sydney Airport said it is assisting the AFP, adding: “The airport is operating normally.”

The man has been charged with obstructing and hindering a Commonwealth official, and creating a disturbance at an airport.

He has been granted bail and is due to appear in court at a later date.