"It is not a hijack. One disruptive passenger tried to enter the plane's cockpit," Deputy Transport Minister Abdul Aziz Kaprawi told AFP.
The passenger, a Sri Lankan national who was apparently drunk, was overpowered by the plane's crew and later arrested at Melbourne's airport, he said.
"The passenger... Claimed to have a bomb. But it was not a bomb but a powerbank," Aziz added.
"Everyone on board is safe," Aziz added.
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"He was taken out of the plane handcuffed by Australian security officers."
Malaysia Airlines confirmed the plane was forced to return to Australia and had safely landed in Melbourne.
"MH128 safely landed in Melbourne Airport at 11:41pm," the airline said in a statement. "Safety and security are of Malaysia Airlines' utmost priority.