The 25-year-old man who threatened to blow up a Malaysia Airlines plane on its way from Melbourne to Kuala Lumpur had a history of mental health problems, Australian Prime Minister Malcolm Turnbull said today.

"I can confirm that the matter is not currently being treated as terrorism-related," Turnbull told parliament. 

"I am informed the man has a criminal history and has previously been treated for mental health issues.

"Police also said the man, identified as Manodh Marks, had been released from psychiatric care on the same day he purchased his ticket and boarded the flight.

The mid-air drama on Flight MH128, with 337 passengers on board, occurred late Wednesday about 20 minutes after take-off, when the Sri Lankan man tried to enter the cockpit, claiming to have a bomb.

He was overpowered by crew and passengers and the plane returned to Melbourne for an emergency landing.

The man, who is on a student visa in Australia, was arrested and charged with endangering the safety of an aircraft and making false threats.

The Australian Associated Press said he refused to face court on Thursday, with his lawyer conveying fears for his safety in custody.

"He does have concerns for his safety in custody," defence lawyer Tess Dunsford told the magistrate, adding her client suffers from a psychiatric illness and would not be applying for bail. 

"Malaysia Airlines would like to stress that at no point was the aircraft hijacked," the airline said on a statement today.

Passenger Scott Lodge told Australian Associated Press that the man grabbed a flight attendant by the arm and she screamed out for help.

"In that one second, there were four of us out of our seats and we pounced on him, he just didn't expect it at all," he said.

"All of a sudden, someone has him in a chokehold and got his arm behind his back, and the other guy eventually choked him and he passed out."

According to former Australian football league player Andrew Leoncelli, who was on board, the man screamed "I've got a bomb and I'm going to fucking blow the plane up" before flight attendants and other passengers tackled and restrained him.

Leoncelli told Fairfax media that he was holding a "giant black object" on his hand, which police later said was a bluetooth speaker or something similar.

Local media reported that Melbourne airport was in lockdown when the plane landed and other flights were diverted away to nearby airports.

Police said the aircraft has been moved to a secure location for further checking, while the passengers were allowed to leave after eight hours of being kept in an isolated room in the terminal.

Some of the passengers criticised police handling of the incident, saying they were inside the plane on tarmac for more than 80 minutes, unsure if there was a bomb on their plane.

"If there was a bomb on that plane we should have been evacuated from it. 

"Instead, we sat there," Stan Young, a passenger, said.

Victoria Police chief commissioner Graham Ashton said the police needed to take "all possibilities into account," since they thought the offender may have had accomplices or other explosive devices.

"If we had an incident where there were further explosives that were triggered, we could have had a mass casualty incident. There were 337 passengers on that plane, plus crew," Ashton told reporters.

- dpa