Heavily armed police have been called to a plane at Melbourne Airport after a man who was carrying a plastic bag claiming to have a bomb inside tried to enter the cockpit of the Malaysia Airlines flight.

Flight MH128 from Melbourne to Kuala Lumpur was forced to turn back to Melbourne shortly after take-off at 11:11pm on Wednesday when a 25-year-old student from Sri Lanka tried to enter the cockpit, police said.

Key points: A Dandenong man, 25, shouted he had a bomb and tried to get into the cockpit, police say

A Dandenong man, 25, shouted he had a bomb and tried to get into the cockpit, police say The plane turned back to Melbourne after at least one passenger and crew tackled him

The plane turned back to Melbourne after at least one passenger and crew tackled him He was arrested by tactical police on landing and has been taken into custody

He was arrested by tactical police on landing and has been taken into custody The man had an "electronic device" that was not an explosive, police say

The man, who has been living in Dandenong in Melbourne's south-east, was tackled by crew members and several passengers, who overpowered him and tied him up with belts.

Heavily-armed police wearing helmets and body armour and carrying rifles boarded the aircraft after it landed just before midnight, and placed the man under arrest.

Victoria Police later said the incident was not being treated as terrorism.

Sorry, this video has expired Anxious parents describe hearing Malaysia Airlines plane was forced to return after bomb threat

They said the man was known to have a history of mental illness.

Victoria Police Chief Commissioner Graham Ashton said the man was carrying a "speaker-type device".

"It looked to me like a slightly larger version of an iPhone … as one of these Bluetooth-type speakers. It has cords that allow you to plug it into some sort of phone device to play music on," he said.

Commissioner Ashton said the man was released from psychiatric care on Wednesday.

A man is detained on the floor of a plane, held down by a flight attendant. ( Twitter: Saroki19 )

He said the man was likely to face Melbourne Magistrates' Court later today.

Victoria Police Superintendent Tony Langdon earlier praised those onboard for subduing the man.

"We are obviously concerned for the passengers and crew. It would have been a very traumatic experience for them.

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"I would say that it would have been quite heroic for the crew and passengers to restrain this person."

Passenger Laura, who asked her surname be withheld, said she feared the worst when the drama unfolded.

"Honestly, when they were trying to get him down to the ground, and there was a lot of screaming, I genuinely did think that was it," she said.

"I thought the plane was going to go down, I thought the bomb was going to go off, I really did think I was going to die."

Police have interviewed passengers about the incident.

"They'd be very concerned. They're tired. They've had their plans disrupted. I can't praise them highly enough," Superintendent Langdon said.

"They've been wonderful in their co-operation with us and we just hope that they have a wonderful journey after this."

Superintendent Langdon said he believed security measures at the airport were appropriate.

"The circumstances are that the gentleman stated he had a device, and he had a piece of equipment which, for all intents and purposes, is something that everybody would be carrying around on a daily basis," he said.

He would not go into any further detail about the object, except to say it was an "electronic device".

"It was quite quickly ascertained it wasn't an explosive device," he said.

Federal Transport Minister Darren Chester also backed Melbourne Airport's security systems.

"From the early reports I have received from the Office of Transport Security, the screening equipment was in place and working at the time," he said.

"100 per cent of passengers and baggage are screened before a flight takes off.

"Let's wait and see what the details of the alleged device is and was and go from there."

Object 'had antennas coming off it'

Former AFL player Andrew Leoncelli told the ABC he was near the front of the plane and saw a man carrying a big object go towards the cockpit and become really agitated.

A passenger ducks as police enter the plane. ( Supplied: Andrew Leoncelli )

"I ran to the front and confronted him around the corner and he was there and he was a tall guy, taller than me with a beanie on, wearing dark clothing, dark skin, carrying a giant thing, a very strange-looking thing with antennas coming off it, saying, 'I'm going to blow the plane up, I'm going to f***ng blow the plane up'."

He said the man then ran to the back of the plane, where he was overpowered by other passengers.

"Staff grabbed the object, which we're not sure what it was, he was claiming to blow the plane up with, and walked it back to the front of the plane."

The plane was parked in a remote bay after it landed. The Australian Federal Police said they were investigating the incident.

"There appears to be no imminent threat to passengers, staff or public and the investigation is ongoing," Senior Constable Adam West said.

The airport was closed during the incident but has now reopened.

Cabin crew screamed for help as drama unfolded

Australian Al Jazeera reporter Drew Ambrose was on board the plane and told the ABC a male passenger carrying what appeared to be an electronic device tried to run into the cockpit just after the plane took off.

Mr Ambrose, who works for Al Jazeera in Kuala Lumpur, said the man then ran to the back of the plane, where about half a dozen passengers stopped him, using belts to restrain him.

Sorry, this video has expired Superintendent Tony Langdon describes the Melbourne Airport bomb threat drama

Arif Chaudhrey was also onboard the flight and helped stop the man.

"Staff screamed 'help, help help' ... I was about four to five seats from where it happened," Mr Chaudhrey told the ABC.

"A couple of us guys quickly jumped to grab that guy.

"The staff [got] a spare seatbelt so we handcuffed him at the back, his legs and hands, and put his face on the floor."

The passenger was restrained by the time police entered the plane. ( Supplied: Andrew Leoncelli )

Passengers still stuck inside airport

In a statement, Malaysia Airlines said the aircraft turned back "after the operating Captain was alerted by a cabin crew of a passenger attempting to enter the cockpit".

"Malaysia Airlines would like to stress that at no point was the aircraft 'hijacked'," it continued.

"MH128 safely landed in Melbourne airport at 11.41pm.

"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.

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"Passengers have safely disembarked the aircraft and will be screened by Australian authorities.

"The airline wishes to apologise for the inconvenience caused."

Passengers who were onboard the flight were placed in a holding area inside Tullamarine Airport from about 2:00am and were only allowed to leave just after 9:00am.

The airport was closed for some time but has reopened.

Passenger Don Urwin said he heard crew members call for passengers to help to grab the man.

"You don't think it can happen in this country, but it does and you just move on and fortunately we're all safe," he said.

Police close a road into Melbourne airport after an incident on a Malaysia Airlines plane. ( ABC News: Iskhandar Razak )

Melbourne Airport officials said some flights could have minor delays.

Family members at the airport said they had been texted by loved ones on the plane to come and collect them when the plane returned.

"For about an hour and a half and they [the passengers] were very scared because it happened right in front of them and they were just told to sit in their seats and not move while this guy was screaming and causing havoc," said one mother, whose daughter was on the flight.

"People were crying and screaming."

Superintendent Langdon said the plane would be subject to checks, but had been handed back to Malaysian Airlines.