MELBOURNE, June 1 (Xinhua) -- A Malaysia Airlines flight bound for Kuala Lumpur was forced to return to Melbourne on Thursday after a passenger who claimed to have a bomb tried to enter the cockpit.

Flight MH128 turned around when a 25-year-old man from Dandenong, southeast of Melbourne, tried to enter the cockpit shortly after take-off.

Victoria Police boarded the plane after it landed back at Melbourne and successfully subdued and arrested the man without incident.

Witnesses on board the plane said the man was tackled by two crew and at least one passenger after he approached the front of the plane with a "strange looking" object.

Andrew Leoncelli, a passenger on the flight, said the device had several aerials protruding from it.

"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," Leoncelli, a former Australian Rules footballer, told Australian media on Thursday.

"I've never seen anything like it. It was the size of a watermelon, it was huge, it was black."

"It had two sort of like antennae stuff coming off it, but it also looked like it had an iPhone jack in it, so it could have been just like a beatbox thing."

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

They said that the man was known to police as having a history of mental illness.

"We do not believe this is terrorist-related," Victoria Police superintendent Tony Langdon told reporters.

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

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

Langdon said the device the man was carrying was an "electronic device, but it was quickly ascertained that it was not an explosive device."

Leoncelli said a group of male passengers held the man on the floor "with eight feet" on his back, legs and head.

Darren Chester, Australia's transport minister, joined Langdon in praising passengers as heroes.

"It's worrying obviously for the passengers and crew on board," Chester said on Thursday.

"I want to thank passengers for the action they took in subduing the unruly passenger.

In a statement, Malaysia Airlines said the aircraft turned back to Melbourne "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'.

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

Passenger Laura, who asked that her surname be withheld, said she feared the worst.

"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."

The airport was closed for a time after the incident but has since re-opened.