Mr Abbott moved a condolence motion in the House of Representatives on Wednesday, offering the Parliament's "severe condolence for the families and loved ones of the six Australians and the other passengers and crew who are presumed to have died''. Labor leader Bill Shorten backed the motion.

The families of Queensland couples Cathy and Bob Lawton, and Rodney and Mary Burrows, who were on board the plane, were in the public gallery on Wednesday.

"Madam Speaker, we mourn all those 239 passengers and crew," he said.

"We especially mourn the six Australian citizens and the one Australian resident who must be presumed dead and we grieve with their families and loved ones.

The Prime Minister said four Australian families had "an ache in their heart" and "nothing we can say or do can take that ache away".

"Still, the knowledge that this nation, through this Parliament, has paused to acknowledge that loss, may be of some comfort in facing this terrible bereavement," he said.

Mr Abbott said 12 aircraft and two ships were continuing the search in the southern Indian Ocean on Wednesday to find any trace of wreckage from the Boeing 777.

He said black box recovery equipment was on its way to Australia and would be deployed to the search area by an Australian navy ship.

Mr Abbott said he had pledged to Malaysia's Prime Minister Najib Razak Australia's ongoing assistance to the investigation, which has struggled over days of bad weather.

"The crash zone is about as close to nowhere as it's possible to be but it's closer to Australia than anywhere else," he said.

Mr Abbott said a considerable amount of debris had been sighted in the area where the flight was last recorded.

"Bad weather and inaccessibility has so far prevented any of it being recovered but we are confident that some will be," he said.