The brother of a Brisbane man on the missing Malaysia Airlines jet says the hijacking theory brings its own torment.

The brother of an Australian man aboard the missing Malaysia Airlines flight says talk of a hijacking has left him with some hope.

But David Lawton says the theory has also brought torment and he’s desperate to learn the truth about his brother’s fate.

Bob Lawton and his wife Cathy were among six Australians on the Malaysia Airlines jet that vanished from radar screens on March 8.

The Boeing 777 had taken off from Kuala Lumpur for Beijing but never arrived, sparking a massive international search operation.

Authorities say it is now clear the flight was deliberately diverted by someone on board, with attention focused on the flight crew and the hijacking theory.

David Lawton, who lives just south of Brisbane, says the lack of surety about his brother’s fate is agonising.

“Maybe it’s been hijacked. That gives me hope but in this day and age, with the technology we have, you’d think they’d be able to find it, but apparently no,” he told the ABC on Monday.

He says the prospect of a hijacking is also frightening.

“While you’ve got hope, you’ve got worries too. Because if they’re alive, are they being treated well, or what’s happening?” Mr Lawton has told Fairfax Media.

He said the family was getting daily briefings from Australian officials.

David Lawton said the constantly changing picture about what had happened to the plane was like being on a roller coaster ride, with no way to get off.

“It’s been a blur really, one story after another, you don’t know what to believe,” he told the ABC.

“There’s so many different thoughts going through my head all the time. One moment it might be that they’re alive, the next I’m thinking they’re gone.”

He said the mystery was taking a heavy toll on his parents, who were both in their 80s.

“They’re just trying to get through one day at a time.”