Take offs from the Melbourne Airport have been halted for the time being.
"I just heard shouting, there was a bloke saying he wanted to speak to the captain and cabin crew were trying to calm him down. He goes, "no, I'm not going to sit back down - I'm going to blow the plane up" he said. Others passengers described it as an "electronic frequency" device.
Armed security personnel entered the plane to remove the disruptive passenger and then escort the others out, he said.
Pilots made a return to the airport after a passenger reportedly attempted to gain access to the cockpit, claiming that he had an explosive device on his person.
While passengers suggested he was armed with a "detonator".
No-one is believed to have been injured.
A Malaysia Airlines plane was forced to return to Melbourne in Australia after a passenger tried to enter the cockpit.
It confirmed that the "disruptive passenger" tried to enter the cockpit, but stressed "at no point was the aircraft "hijacked".
It said Flight MH128 landed after being airborne for 14 minutes. Local media reports in Melbourne said the airport was in lockdown temporarily.
"Passengers have safely disembarked the aircraft and will be screened by Australian authorities.The affected passengers will be accommodated at hotels".
Saiqa Chaudhery, whose husband was on the flight, told Channel NewsAsia that other passengers then "tackled (the passenger) down and tied him" up.
The plane landed back at Melbourne just before midnight and was parked in a remote bay.
She said her boyfriend, who is yet to be identified, had asked her "call everyone" because passengers could see police on the tarmac but that there was "no people coming in to get them".
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.