Passengers on how they took on and tied up a threatening man in mid-air

A man being detained after bomb threats were made on board a Malaysia Airlines flight to Kuala Lumpur from Melbourne. Photo / AAP

Brave passengers staged a mid-flight retaliation against a would-be bomber, binding his hands and planting their feet on him after he threatened an international flight out of Melbourne.

Malaysia Airlines Flight 128 abandoned its planned trip to Kuala Lumpur and turned back to Tullamarine Airport, Australia, where terrified passengers were forced to wait about another 80 minutes before authorities stormed the aircraft.

Police, carrying semi-automatic assault rifles and wearing body armour, boarded the plane, removed the offender and an object he claimed was explosive.

The mentally-ill man threatened to detonate a bomb and attempted to enter the cockpit, police said today.

"He had been released from psychiatric care from the Monash Medical Centre (yesterday), and from there, we believe he has purchased a ticket on this plane," Chief Commissioner Graham Ashton told reporters.

Former AFL player Andrew Leoncelli says the man had a "boombox" the size of a watermelon before passengers tackled him, tied him up and held him down.

"He had eight shoes sitting on his face, his back and his legs... (they) jammed him in between the row and they stuck their feet on him," he told 3AW today.

Leoncelli said passengers endured a terrifying wait for police, unsure if there was a bomb on board.

"Everyone was s***ing themselves," he added.

"He was saying: 'I'm going to the blow the f***ing plane up, I'm going to blow the plane up,"' Leoncelli told ABC. "He was agitated, is the best description -100 per cent, he was agitated."

Passenger Selena Brown said the passengers weren't going to let the man cause a problem.

"It was brilliant (a) typical thing for Australians to do," she told reporters.

Passengers were calm but unhappy about how long it took police to get onto the plane, Brown said.

"We were more worried about long it has taken for the police to arrive. How long? How long? We could see them sitting outside."

Victoria Police Superintendent Tony Langdon would not say how long police waited to board the plane.

"We have a standard procedure in relation to these matters and at times we will be slightly delayed in what we need to do purely because of concerns in relation to the passengers," he told reporters.

"You can appreciate that an aircraft is quite a complex piece of equipment. So we have to make sure that we're doing everything humanly possible to not further endanger passengers, crew and (the) person apprehended."

Langdon said: "We believe that the actions of the passengers and crew were quite heroic. They managed to calm the situation, allow the aircraft to return safely and we can't commend them highly enough."

Passengers Stan and Pam Young were on MH128 starting a trip to London when the trouble unfolded and knew nothing of the bomb threat until hours later when they disembarked and were searched before being taken to an isolated terminal room.

"It took two hours for them (police) to come. We sat on the tarmac waiting not really knowing what was going on," Pam Young said.

"If there was a bomb on that plane we should have been evacuated from it. Instead we sat there," Stan Young said.

A 25-year-old Dandenong man is in custody. He has a history of mental illness, police said.

The man did not have a bomb and police are not treating the incident as a terrorist act. There were no injuries.

- AAP, AP