PETALING JAYA • A Malaysia Airlines (MAS) flight bound for Kuala Lumpur was forced to make a U-turn back to Melbourne last night after a "disruptive passenger" claimed he was carrying a bomb.

Flight MH128 left Melbourne's Tullamarine airport at 11.11pm (local time) and was due to arrive at 5.28am (Malaysia time) in Kuala Lumpur.

A statement released by the Malaysian national carrier said the flight turned back to Melbourne "after the operating captain was alerted by a cabin crew of a passenger attempting to enter the cockpit".

The plane landed in Australia 30 minutes after its departure.

Agence France-Presse quoted Malaysian Deputy Transport Minister Abdul Aziz Kaprawi as saying: "It is not a hijack. One disruptive passenger tried to enter the plane's cockpit."

He added: "The passenger, a Sri Lankan national, claimed to have a bomb. But it was not a bomb but a powerbank."

MAS said MH128 landed safely at Melbourne Airport at 11.41pm, adding that "the aircraft is currently at the remote bay and waiting for security assistance to arrive".

Flights to Melbourne airport were being diverted in a lockdown, according to reports.

The Age, quoting a recording of air traffic control posted online, said a male voice could be heard saying: "We have a passenger trying to enter the cockpit."

About three minutes later, the same male voice said the passenger was "claiming to have an explosive device, tried to enter the cockpit, has been overpowered by passengers".

"However we'd like to land and have the device checked," the pilot said.

SBS News journalist Brianna Roberts tweeted: "Passenger says the man was holding an 'electronic frequency' device, not a bomb. Police on scene now."

She added that on-board announcements called the incident a "security situation".