An operation is underway at Sydney Airport after a firearm was discharged as federal police officers attempted to arrest a man inside a domestic terminal.

A crime scene has been sectioned off in the T2 terminal. 

The ABC understands the man was being detained by officers in a struggle when the police gun was fired. 

The Australian Federal Police (AFP) confirmed the man had been arrested.

Crime scene at Sydney Airport after gun goes off

The area has been taped off as a crime scene.  (ABC News: Ethan Rix)

“An investigation into the incident has been launched … and there is no ongoing threat to the public,” a spokesperson said. 

“Further comment will be provided at an appropriate time.”

In a statement, Sydney Airport said it was assisting the AFP following the incident.

“No injuries occurred as a result of the incident. An arrest has been made and the airport is operating normally,” it said.

‘He went for the gun’, eyewitness says

One passenger, who did not wish to be identified, told the ABC he saw “people running” as the gun went off.

“I heard the shouting, I didn’t see what incited it, but he went for the gun,” he said.

“When they hit the ground the gun went off. It looked like [the bullet] hit the wall of that cafe there.

“There were a lot of cops, people running and Jetstar staff ushering people away.”