A Victorian airport has been locked down after a man carrying a gun was detained after boarding a Jetstar flight bound for Sydney.

Vision obtained by 9News shows the man being detained by a passenger and the plane’s pilot on board the plane at Avalon Airport in Geelong, with police called to the scene about 2.50pm.

The man, who was dressed in a high-vis uniform, was seen in a headlock by another man.

People on board the plane removed several items from a tool belt around the man’s waist.

The stock of a shotgun was seen at his feet.

Once he was restrained, a flight attendant could be seen carrying the butt of the shotgun off the aircraft.

9News understands the pilot first noticed the weapon, alerting others to the danger, after the man tried to get on the plane.

It is understood he avoided security and arrived from the tarmac, claiming he needed to do maintenance.

The frightening incident took place on Jetstar flight JQ 610 headed for Sydney.

Witnesses told 9News the incident left them terrified.

“A lot of people start crying, getting freaked out,” a witness said.

“I tried hugging my mum, keeping her safe.”

The entire terminal shut down as passengers were taken off the plane.

The man was lead in handcuffs to a waiting police wagon.

Investigators are working out how a man with a shotgun could get anywhere near a passenger jet.

Nobody was injured in the incident.

Avalon Airport is currently closed, with no one allowed to enter or leave.