It could take up to 48 hours to confirm that debris spotted by satellite 2,500km south-west of Perth belongs to the missing Malaysia Airlines flight MH370, an expert said.
Mr Michael Daniel, a retired United States Federal Aviation Administration official told The Straits Times: "If they have a strong feeling or indication that the debris belongs to the aircraft, one of the first things authorities will do is drop sonar buoys in the water.
"If the black box is there, the buoys should be able to pick up the signals. This could take up to 48 hours but it all depends on how near or far the ships and other assets are."
A sonar buoy is a device equipped with an acoustic receiver and a radio transmitter that emits radio signals when it detects underwater sounds.
The battery in the black box typically runs for 30 days.
Australian authorities said on Thursday there is a possiblity they spotted debris belonging to MH370 which has now been missing for 13 days.
Two objects, the larger of which was measured at 24 metres, were found floating in the Indian Ocean, Australian officials said.
"The objects are relatively indistinct. The indication to me is of objects that are of a reasonable size and probably awash with water and bobbing up and down over the surface," Australian Maritime Safety Authority official John Young told a press briefing in Canberra.
"The largest... was assessed as being 24 metres. There is another one that is smaller than that."
Australia has sent four search aircraft - including one each from the US and New Zealand - and two ships to the area where the debris was located while another merchant ship has also been asked to go there. It takes four hours for an aircraft flying out of base in Perth to reach the location.
