"MH128 had not at any point been hijacked" - MAS

A Malaysia Airlines flight from Melbourne to Kuala Lumpur returned to the Australian airport shortly after take off late on Wednesday after a passenger attempted to enter the cockpit, authorities said.

Passengers and crew on Flight MH128 tackled the man and tied him up with seat belts until the flight landed, one witness told Reuters.

The plane landed safely and the man was apprehended by airport security, said Malaysia Airlines, which is still recovering from two major airline disasters in recent years.

Police said the incident was not terrorism-related and a 25-year old man, understood to be an Australian citizen, had been taken into custody.

"It was an isolated incident and we do believe he suffers from a mental illness," Superintendent Michael Goode of the Australian Federal Police told a media conference on Thursday.

Arif Chaudhery, a passenger on board MH128, told Reuters that about 30 minutes into the flight a male passenger attacked a female member of the cabin crew who screamed out for help.

"Some passengers and crew grabbed the man and tackled him to the floor," Chaudhery said, adding that seat belts were used to tie the man's hands.

"We were very lucky. It could have been worse."

Armed security personnel entered the plane to remove the man and escort other passengers off the aircraft, he said.

INVESTIGATION BEGUN

The airline stressed the flight had not at any point been hijacked.

Flight MH128 returned to Melbourne's Tullamarine Airport "after the operating captain was alerted by a cabin crew of a passenger attempting to enter the cockpit", the airline said in a statement. It had departed at 11:11 p.m. Melbourne time and returned at 11:41 p.m.

"Malaysia Airlines together with the Australian authorities will be investigating the incident," the statement added.

Aircraft tracking website Flightradar said flights bound for Melbourne had been diverted to other airports because of the incident.

Melbourne's Tullamarine airport was briefly closed during the incident but has since reopened, airport authorities said.

Malaysia Airlines has suffered two major airline disasters in recent years. In 2014, Flight MH370 with 239 people on board went missing on its way from Kuala Lumpur to Beijing.

The Boeing 777 plane has yet to be found and its location is one of the world's greatest aviation mysteries. The deep-sea search for the missing plane was called off in January.

Soon after MH370 went missing, Flight MH17 from Amsterdam to Kuala Lumpur was shot down in eastern Ukraine, killing all on board.

The airline has struggled to recover from the twin tragedies, having to cut staff and restructure its business as passenger numbers fell.