Mr Truss addressed reporters on Saturday afternoon at the Pearce Royal Australian Air Force base north of Perth, which has become a major international rallying point in the search for missing flight MH370.

"It is the most promising lead available internationally but there are any number of other explanations about what might of been sighted as a result of this satellite imagery," Mr Truss said.

"Even though this is not a definite lead, it is probably more solid than any other lead around the world and that's why so much effort and interest is being put into this search."

Royal Australian Air Force group captain Craig Heap said there was a ‘‘reasonable’’ chance of finding something in the Indian Ocean in the search.

In recent days 15 flights have canvassed a search area in the Southern Indian Ocean, about 2500km south-west of Perth, in pursuit of two objects captured by satellites on Sunday.

VIDEO: Acting Prime Minister Warren Truss addresses the media about the ongoing search for Malaysia Airlines flight MH370.

Mr Truss conceded the four-day lag between when the objects were detected and when the search was launched on Thursday has complicated exploration efforts.

"The fact that it’s six days ago that this imagery was captured does mean that clearly what objects that were there are likely to have moved a significant distance as a result of current and winds," he said.

"Its also possible of course that they've just drifted to the bottom of the ocean bed, and the ocean in this area is between three and five kilometres deep."

He said it had taken four days for authorities to understand potential significance of the objects in the satellite images.The search zone was increased from an initial area of 25,000km to 36,000km on Saturday. 

The Australian search effort has covered about half a million square kilometres over the past few days.

Additional aircraft and ships were being sent to RAAF Pearce from around the world to assist, including a New Zealand Orion and a US Navy Poseidon which arrived this week, two Chinese planes that were due to arrive Saturday and a Japanese plane due Sunday.

‘A pair of eyes’ the best chance of a discovery

Despite the incredible technological capacity of the planes destined for the Southern Indian Ocean via RAAF Pearce, the best chance of finding the objects was "visual", or put plainly, through use of the human eye, Mr Truss said.

"It is more likely that a pair of eyes is going to identify something floating in the ocean than the technical equipment that is onboard these aircraft," he said.

The Chinese IL76 planes were well equipped in this regard, as they have a lot of windows and room to carry a lot of bodies, Captain Heap said. 

"Both those aircraft are large transport aircraft that have a very good visual search capability," Captain Heap said.

"What we're looking for is human eyes actually spotting something in the water: you need to be low, you need to be close and you need to be there as long as you can."

Abbott announcement defended

Mr Truss backed Prime Minister Tony Abbott's decision to interrupt parliamentary question time on Thursday to declare the satellite find a credible lead, despite the fact that two days later Australia is no closer to finding the objects, let alone determining what they are.

"The Prime Minister's statement in the parliament was correct," Mr Truss said. 

"This was a discovery of interest and his statement yesterday was also correct, namely that are a lot of other possible explanations for this satellite imagery."

Australian authorities have been in contact with Malaysia every few hours and Malaysian military officials have been posted in Australia during the search operation, but has not sent any planes to assist with the Indian Ocean search.

Search to continue ‘indefinitely’

Mr Truss would not say how much the search effort was costing Australia.  "This particular disaster has come to our sector of the globe and we will undertake our responsibility to the people who were on board the global community," he said.

If the debris were to be located it could be retrieved by warships and other maritime assets already in the area, Captain Heap said.

The Australian government has no contingency in place for ending the search, which would continue "indefinitely", Mr Truss said.

"This is a credible lead and it’s in Australia's search and rescue area so we take our responsibilities very seriously to check out this lead," he said.

"We will take it one day at a time, we have no contingency plans to end the search any time soon, we'll keep going as long as there's hope.