Thoughts with those on Malaysia flight: PM

Prime Minister Tony Abbott says Australians' thoughts are with the passengers and families of those on a missing China-bound Malaysia Airlines jet.

Queensland couples Catherine and Robert Lawton and Mary and Rodney Burrows, and Sydneysiders Li Yuan and Gu Naijun, are among 239 people on board flight MH370, which disappeared between Malaysia's east coast and southern Vietnam.

Mr Abbott on Sunday described the tragedy as a "horrible, horrible business".

"Our thoughts and prayers are with the passengers and their families on that ill-fated aircraft, particularly to the six Australian passengers and their families, that have now been confirmed to be on board," he told reporters in Adelaide.

"We're looking at ways in which we can help with the search and recovery operation."

Opposition leader Bill Shorten echoed Mr Abbott's comments.

"I believe the Australian nation's thoughts go out to the families of those Australians and New Zealanders that are on this plane, and indeed the families of everyone," he told reporters in Melbourne.