An armed teenager boards a commercial plane in Melbourne before being subdued by the crew.

A teenager carrying a rifle managed to climb aboard a commercial plane at an airport near Melbourne in Australia before being subdued by the plane's crew and passengers.

The 17-year-old entered Avalon Airport's runway on Thursday through a hole in the site's fence and headed towards the plane carrying around 160 passengers.

Michael Reid, a local police official, told reporters, "He climbed the front stairs and made his way to the front of the plane. Passengers then noticed he had a rifle, and he was subdued by three passengers."

No one was injured in the incident, and the teenager has been placed in custody pending investigation.

He was not known to the police, and it appears to be a lone act. The police are collaborating with the counter-terrorism unit, but his motives are still unknown.

Reid mentioned "finding ammunition with the rifle."

The plane, operated by Jetstar, a low-cost subsidiary of the Australian airline Qantas, was supposed to fly between Melbourne and Sydney.

Reid added, "It is concerning that someone could breach security rules, approach an aircraft, board it, and have a firearm in their possession."

Footage aired by Australia's Channel Nine showed a young man wearing a green vest similar to those worn by airport ground staff being held on the ground by a passenger and a crew member.

A flight attendant carrying what appears to be the lower part of the rifle walks past them.

Jetstar stated in a release that they are cooperating with the police and airport authorities to investigate the incident, noting that "the situation could have been very challenging" and expressing "deep gratitude to the customers who assisted the crew in controlling the situation."

It is not yet known whether the teenager was the one who created the hole in the airport's security fence or if the gap was already there.