Australian leader Tony Abbott says authorities are confident that signals heard in the Indian Ocean are coming from the "black box" flight recorders of the missing Malaysia Airlines plane.
Speaking in China, he said teams had "very much narrowed" the search area.
An Australian vessel has on four occasions picked up signals consistent with flight recorders, officials say.
But a fifth signal picked up by a plane on Thursday is now thought unlikely to be linked to flight MH370.
Flight MH370 vanished on 8 March, with 239 people on board. It was flying from Kuala Lumpur to Beijing when it lost contact with air traffic controllers.
Based on satellite data, officials believe it crashed into the southern Indian Ocean, far from its intended flight path.
Speaking in China during an official visit, Mr Abbott said search teams needed as much information as possible from the acoustic signals before the black box batteries ran out.
"It's [the search area] been very much narrowed down because we've now had a series of detections, some for quite a long period of time,'' Mr Abbott said.
"Nevertheless, we're getting to the stage where the signal from what we are very confident is the black box is starting to fade."
On Thursday an Australian aircraft picked up an audio signal in the same area as the four previous detections.
But the Australian Joint Acoustic Analysis Centre had analysed the data and confirmed that the signal was "unlikely to be related to the aircraft black boxes", said Air Chief Marshal Angus Houston, who heads the agency overseeing the search.