Australian Prime Minister Tony Abbott has said that he is confident signals detected in the Indian Ocean in the past week were from the black box of missing Malaysia Airlines flight MH370.
However, speaking at a news briefing in Beijing, he added that the signals from the transmitter were "rapidly fading" and the search area needed to be narrowed as soon as possible.
He also revealed that that finding the jet in the Southern Indian Ocean would be a "massive, massive task".
Five underwater 'pings' have been heard from what are believed to be the aircraft's black boxes - but there have been no new signals since early last week.
The battery life of a black box usually lasts for only a month so, with just a few days before the box falls silent, time is running out in the hunt for the missing plane.
Mr Abbott said: "No one should underestimate the difficulties of the task still ahead of us.
"Trying to locate anything 4,500 metres (15,000 feet) beneath the surface of the ocean, about a 1,000km (620 miles) from land is a massive, massive task.
"Given that the signal from the black box is rapidly fading, what we are now doing is trying to get as many detections as we can so that we can narrow the search area down to as small an area as possible."
Mr Abbott did, however, say that search teams are within a kilometre of the plane's final resting place - which could be 14,700ft under water.
“It is probably the most difficult search in human history.
“We’re getting to the stage where the signal from what we’re very confident is the black box is starting to fade.
"We’re hoping to get as much information as we can before it expires.”