A late night flight has turned back to Melbourne Airport shortly after take-off following a security incident involving a "disruptive" and "threatening" passenger who tried to enter the plane's cockpit while carrying an unidentified black object, according to the airline and local police.

One fellow passenger described seeing the man behaving erratically before pinned to the floor by airline staff.

The Malaysia Airlines flight has since landed safely and the passenger has been apprehended by airport security. Dramatic photographs taken by other passengers on board the flight showed heavily armed security personnel boarding the plane after its return to Melbourne. 

A statement from the airline said Flight MH128, which left Melbourne for Kuala Lumpur at 11.11 pm, was turned back "after the operating captain was alerted by a cabin crew of a passenger attempting to enter the cockpit."

In air traffic control audio posted online, a male voice can be heard saying: "We have a passenger trying to enter the cockpit."

About three minutes later the same male voice can be heard saying the passenger was "claiming to have an explosive device, tried to enter the cockpit, has been overpowered by passengers."

"However we'd like to land and have the device checked," the voice says.

Victoria Police said in a statement the man had allegedly threatened the safety of passengers and staff before being subdued. 

Former AFL player Andrew Leoncelli was sitting in business class, several seats away from the cockpit, when the incident unfolded. He said a man carrying a large black cylindrical object ran towards the cockpit just after the plane took off.

Mr Leoncelli asked the man what he was doing and contemplated wrestling with him, however the man became agitated and started running up and down the aisle.

The man was then pinned to ground by staff after a brief scuffle, he said, with staff taking away the black object as the plane turned back to Melbourne.

When the plane landed, passengers were left on the tarmac for around 90 minutes, with very little information from airline staff about what was happening.

Eventually, heavily-armed security staff wearing camouflage uniforms and helmets entered the plane and removed the man.

As he waited on the plane, Mr Leoncelli recorded a video.

"There's a giant black object on this plane, a crazy guy wants to blow it up, who was subdued," he said.

"The police are sitting four kilometres away, haven't moved in 25 minutes. This is an absolute joke. Seriously, help us."

During the lengthy wait on the tarmac, others took to Instagram to express their frustration and fear.

"We have been waiting in the plane for an hour, still waiting for the police," one passenger wrote. "The bomb may go off any time."

Malaysia's Deputy Transport Minister Datuk Seri Ab Aziz Kaprawi was quoted in The Star, a local news outlet, saying the passenger was drunk and that the object he was holding was a "powerbank", not an explosive device.

MH128 landed safely at Melbourne Airport at 11.41pm, the company said. 

"Following the incident on MH128, the disruptive passenger has been apprehended by airport security. Malaysia Airlines together with the Australian authorities will be investigating the incident," the airline said.

Malaysia Airlines stressed that "at no point was the aircraft 'hijacked'."

Flights to Melbourne airport were being diverted, according to the 24-hour aviation monitoring website Flight Radar.

Victoria Police said there was "no imminent threat to passengers, staff or public and the investigation is ongoing."

More to come