A Malaysia Airlines plane was forced to make an emergency landing at Melbourne's Tullamarine Airport less than 30 minutes into a flight after a man tried to enter the cockpit, claiming to have explosives.
One of the passengers on board told SBS World News he believed the man was carrying an "electronic frequency" device.
Flight MH128 from Melbourne to Kuala Lumpur returned to Melbourne shortly after takeoff late on Wednesday "after the operating captain was alerted by a cabin crew of a passenger attempting to enter the cockpit", the airline said.
In a statement, the airline stressed "at no point was the aircraft 'hijacked'".
"Safety and security are of utmost priority to Malaysia Airlines," the statement said.
"Malaysia Airlines together with the Australian authorities will be investigating the incident. Affected passengers will be accommodated at hotels. They will be offered travel on the next available flight or on other carriers."
Victoria Police said the incident happened four kilometres out of Melbourne when a man left his seat, shouting that he had a bomb and tried to move towards the cockpit.
"He attempted to gain access to the cockpit and was restrained by passengers and crew," a spokesman said on the Nine Network.
"The crews invoked emergency procedures and returned to the airport and Australian Federal Police responded, entering the aircraft and removing that male."
In air traffic control audio posted online, a male voice can be heard saying: "We have a passenger trying to enter the cockpit."
About three minutes later the same male voice can be heard saying 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 voice says.
Drew Ambrose was one of the passengers who helped to restrain the man. He told SBS World News the man was "erratic" and didn't appear to have a plan.
“A guy ran to the cockpit. I heard him yelling at the flight attendant as the plane was talking off,” he said.
“He was carrying something. Then he came to the back of the plane. I asked the flight attendant if she needed help, and she said yes”
“I went to the back of the plane and he was on the floor. A guy had him in a choke hold and we all just restrained his legs. Then they restrained him with belts and put him at the back of the plane.”
“That was the nervous bit as I wasn’t sure what he had on board the plane, and he was still on the plane,” he said.
"Some people wanted to get off the plane because they were worried [a] bomb would go off."
Passenger Andrew Leoncelli told Fairfax the man screamed: "I've got a bomb and I'm going to f***ing blow the plane up" before flight attendants and other passengers tackled and restrained him.
With the suspect in custody, Victoria Police have said they do not believe the attack is related to terrorism.
"What I can tell you about the male is that his history would appear to have mental illness. We do not believe this is terrorist-related at the moment," Superintendent Tony Langdon said.
"We are obviously concerned for the passengers and crew. It would have been a very traumatic experience for them."
According to a report in Malaysia's The Star, Deputy Transport Minister Datuk Seri Ab Aziz Kaprawi said the disruptive passenger, thought to be a Sri Lankan national, was drunk.
The minister said the man was holding a "powerbank", or phone charger, while Mr Leoncelli described it as a "giant black object."
Photographs taken by other passengers aboard the flight showed heavily armed security personnel boarding the plane after its return to Melbourne.
The passenger was apprehended by airport security after the plane landed and was sent to a remote part of the airport.
Police said in a statement the man was speaking to investigators, after being subdued.
Flight tracking website FlightRadar24 said the plane was airborne for just 14 minutes.
The incident forced Melbourne Airport into lockdown, with all other flights were diverted to Avalon, near Geelong.
As passengers began arriving later in the morning, they were met by a noticeable police presence.