Further international resources joined the search on Monday and air crews sighted many objects in the water.

But an Australian Maritime Safety Authority spokeswoman said four orange objects, each more than two metres, sighted on Sunday were later identified as ''fishing equipment and other flotsam''.

Other search crews have reported sightings in the past week that have later been assessed as marine life or junk.

Mr Abbott visited RAAF Base Pearce north of Perth on Monday and reiterated Australia's commitment to the search, but conceded personnel were operating on limited information and conducting a difficult operation.

''We are searching a vast area of ocean and we are working on quite limited information,'' he said. ''Nevertheless, the best brains in the world are applying themselves to this task, all of the technological mastery that we have is being applied and brought to bear here.'''

If anybody could solve the mystery it was the Australian Maritime Safety Authority, he said.

''Until we locate some actual wreckage from the aircraft and then do the regression analysis that might tell us where the aircraft went into the ocean, we'll be operating on guesstimates,'' he said

Mr Abbott said his office was in hourly contact with the search co-ordination centre and was in regular contact with officials in China, Malaysia, New Zealand, the US, South Korea and Japan.

Former Australian Defence Force chief Angus Houston, who has been appointed to head a 20-person joint agency co-ordination centre based out of Perth, was briefed at the RAAF base on Monday morning.

''I will obviously be focused very much on co-ordination,'' he said. ''I'm not here to run the search, I'm not here to do the detailed operational side of things; that's being taken care of by the Australian Maritime Safety Authority and the Defence Force.''

Monday's search of an area about 1850 kilometres south-west of Perth involved 10 aircraft and 10 ships, five times the assets assigned to the search on its first day. There were more than 100 people in the air and about 1000 sailors in the area searching for anything that may be linked to the missing flight. Australian crews have been flying 12-hour missions since the Indian Ocean became the focus of the search nearly two weeks ago.

The Royal Australian Navy vessel Ocean Shield was also due to begin its three-day journey to the search late yesterday, transporting a ''pinger locator''. It is a race against time to find the plane's black box before it stops emitting signals, perhaps as early as four days away.

Mr Abbott said he would not put a time limit on Australia's involvement in the search.

''We owe it to everyone to do whatever we reasonably can and we can keep searching for quite some time to come and we will keep searching for quite some time to come,'' he said.