Malaysia Airlines MH370: Australia predicts long search as signals fading fast

With no new underwater signals detected, Australian Prime Minister Tony Abbott said Saturday that the massive search for the Malaysian jet would likely continue "for a long time" as electronic transmissions from the dying black boxes were fading fast.

Abbott appeared to couch his comments from a day earlier while on a visit to China, where he met President Xi Jinping. He said Friday he was "very confident" signals heard by an Australian ship towing a U.S. Navy device that detects flight recorder pings are coming from the Boeing 777.

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He continued to express this belief on Saturday, but added that the job of finding the plane that disappeared March 8 en route from Kuala Lumpur to Beijing remains arduous.

"No one should underestimate the difficulties of the task still ahead of us," he said on the last day of his China trip. We have "very considerably narrowed down the search area, but trying to locate anything 4.5 kilometres beneath the surface of the ocean about 1,000 kilometres from land is a massive, massive task and it is likely to continue for a long time to come," Abbott said.

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After analyzing satellite data, officials believe the plane with 239 people aboard flew off course for an unknown reason and went down in the southern Indian Ocean off the west coast of Australia.

Search crews are racing against time because the batteries powering the devices' locator beacons last only about a month and more than a month has passed since the plane disappeared. Finding the black boxes after the batteries fail will be extremely difficult because the water in the area is 4,500 metres deep.

The Australian ship Ocean Shield is towing a U.S. Navy device that detects black box signals, and two sounds it heard

Saturday were determined to be consistent with the signals emitted from aircraft flight recorders. Two more sounds were detected in the same general area on Tuesday.

"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," Abbott said. "So that we can narrow the search area down to as small an area as possible."

The underwater search zone is currently a 1,300-square-kilometrespatch of the seabed, about the size of the city of Los Angeles.

The Bluefin 21 submersible takes six times longer to cover the same area as the ping locator. That's about six weeks to two months to canvass the current underwater zone. The signals are also coming from 4,500 meters below the surface, which is the deepest the Bluefin can dive. The search coordination centrehas said it was considering options in case a deeper-diving sub is needed.

The surface area to be searched for floating debris had been narrowed to 41,393 square kilometresof ocean extending from about 2,300 kilometres northwest of Perth. Up to 10 planes and 14 ships were searching Saturday.

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Investigators believe the plane went down in the southern Indian Ocean based on a flight path calculated from its contacts with a satellite and analysis of its speed and fuel capacity.

Separately, a Malaysian government official said Thursday that investigators have concluded the pilot spoke the last words to air traffic control, "Good night, Malaysian three-seven-zero," and that his voice had no signs of duress. A re-examination of the last communication from the cockpit was initiated after authorities last week reversed their initial statement that the co-pilot was speaking different words.

The senior government official spoke on condition of anonymity because he wasn't authorized to speak to the media.