A Malaysia Airlines plane en route to Kuala Lumpur was forced to return to a Melbourne airport after a passenger tried to enter the cockpit.
The Airline says the situation has been resolved safely but has not commented on reports that the trouble maker was claiming to be carrying explosives on board the Airbus A330.
Flight MH128 left Melbourne at 11.11pm (2.11pm BST) local time but was turned around after 14 minutes due to a "disruptive passenger".
It landed back at the city's Tullamarine Airport at 11.41pm.
News Corps Australia report the testimony of passenger who said the man was holding an electronic device and had to be subdued by a scrum of fellow travellers.
Victoria Police Senior Constable Adam West confirmed that officers had met the plane on the runway.
"It is alleged that a man tried to enter the cockpit and threatened the safety of passengers and staff," he said. "The man did not gain entry to the cockpit. The man was subdued and a safety plan was enacted."
"There appears to be no imminent threat to passengers, staff or public and the investigation is ongoing," he added.
Pictures of armed officers boarding the plane were posted on Twitter by Aviation writer Brendan Grainger.
The airline stressed that the aircraft was "not hijacked" and said the attacker had been apprehended by security.
Australian Federal Police boarded the plane to check for explosives. All passengers have disembarked from the plane.
Malaysian Deputy Transport Minister Datuk Seri Ab Aziz Kaprawi told The Star he believed that "the suspect is a Sri Lankan national, and that he was drunk".
Melbourne Airport is on lockdown and all flights have been suspended. Incoming air traffic to Melbourne Airport have been diverted to nearby airports.