Flight MH128 - bound for Kuala Lumpur - was forced to turn back "due to a disruptive passenger", a statement from the airline said.
According to the statement, the captain turned the aircraft around after being alerted to a "passenger attempting to enter the cockpit,” BBC News reports.
The plane has since returned to the ground safely with the pilot requesting security assistance.
Melbourne airport has been placed on lockdown as a result of the incident after local media suggested the passenger claimed to have explosives onboard, the Mirror reports.
