Passengers and crew on a Malaysia Airlines flight from Melbourne to Kuala Lumpur tackled a fellow passenger who attempted to enter the cockpit shouting he had a bomb, authorities and witnesses said.

The 25-year-old man, a Sri Lankan national, was tied up with seatbelts and the flight diverted back to Melbourne following the incident shortly after takeoff late on Wednesday.

Australian police said they did not believe the incident was linked to terrorism, instead citing mental health issues. A device carried by the man as he shouted threats was not dangerous, they said. It appeared to be a bluetooth speaker device.

Arif Chaudhery, a passenger on board MH128, told Reuters that about 30 minutes into the flight a male passenger attacked a female member of the cabin crew who screamed for help.

"Some passengers and crew grabbed the man and tackled him to the floor," Chaudhery said, adding that seat belts were used to tie the man's hands.

"We were very lucky. It could have been worse."

The man arrested for trying to enter the cockpit of a Malaysia Airlines flight is driven into the Melbourne Magistrates Court. Photo: David Crosling/via Reuters

Armed police boarded the plane when it landed back in Melbourne, taking the man, who bought a plane ticket hours after being released from psychiatric care, into custody.

The man is due to appear in court today on charges relating to making threats, false statements and endangering the safety of an aircraft.

INVESTIGATION BEGUN

Malaysia Airlines said it was investigating the incident and all baggage from the flight had been re-scanned by Australian security officials before being forwarded to new flights for the passengers.

"Malaysia Airlines’ technical and cabin crew that operated MH128/31May will not operate on flights until further notice," the airline added in a statement.

Australian authorities are also investigating.

Melbourne's Tullamarine airport was briefly closed during the incident but has since reopened, airport authorities said.

Malaysia Airlines has suffered two major disasters in recent years. In 2014, Flight MH370 with 239 people on board went missing on its way from Kuala Lumpur to Beijing.

The Boeing 777 plane has yet to be found and its location is one of the world's greatest aviation mysteries. The deep-sea search for the missing plane was called off in January.

Just over four months after MH370 went missing, Flight MH17 from Amsterdam to Kuala Lumpur was shot down in eastern Ukraine, killing all on board.

The airline has struggled to recover from the disasters, having to cut staff and restructure its business as passenger numbers fell.