A new acoustic signal has been detected in the hunt for Malaysia Airlines Flight MH370.
The news further boosts confidence that officials are zeroing in on the missing plane after weeks of searching.
The signal, which could be from the plane's black box recorders, brings to five the number of "pings" detected in recent days within the search area in the Indian Ocean.
The first four signals were detected by a US Navy towed pinger locator aboard Australia's Ocean Shield vessel.
The latest was reported by an aircraft picking up transmissions from a listening device buoy laid near the ship yesterday.
The data will require further analysis but it showed the potential of being from a "man-made source", Angus Houston, head of the Australian agency co-ordinating the search, said in a statement.
"Whilst conducting an acoustic search this afternoon a RAAFAP-3C Orion aircraft has detected a possible signal in the vicinity of the Australian Defence Vessel Ocean Shield," Mr Houston said.
Malaysia Airlines Flight MH370 disappeared more than a month ago.
The mystery has sparked the most expensive search and rescue operation in aviation history, but concrete information has proven frustratingly illusive.
The black boxes record cockpit data and may provide answers about what happened to the plane.
It was carrying 227 passengers and 12 crew when it vanished on 8 March and flew thousands of kilometres off its Kuala Lumpur-to-Beijing route.
The batteries in the missing plane's black boxes have already reached the end of their 30-day expected life, making efforts to swiftly locate them on the ocean floor all the more critical.