KUALA LUMPUR, Malaysia - The chief of the team coordinating the hunt for Malaysia Airlines Flight 370 in the Indian Ocean said Monday that an Australian vessel had twice detected underwater signals "consistent with" flight data and cockpit voice recorders, possibly from the missing jet.
"Clearly this is a most promising lead," the official, Angus Houston, said at a news conference in Perth, Australia. He called it "probably the best information that we have had" in the search.
"I'm much more optimistic than I was a week ago," he said.
But he cautioned that determining the nature and source of the signals might take several days.
The two "signal detections," as he called them, occurred within a 24-hour period in the northern part of an area of the Indian Ocean, hundreds of miles off the west coast of Australia, where an international search force has been focusing its efforts in recent days.
The first detection by the vessel, Ocean Shield, lasted about two hours and 20 minutes, he said. The ship lost contact, turned around, then picked up the signal again, hearing "two distinct pinger returns." The second detection lasted about 13 minutes, he said.
But he added that it might take officials several days to confirm that the acoustic noises were from the missing plane.
"This is not the end of the search," he said. "We've still got a lot of difficult, painstaking work to do.
"In deep oceanic water, nothing happens fast," he said.
Even with Houston's caveats, however, the announcement offered the best hope so far that after more than four weeks of fruitless searching across vast areas of sea and land in the Eastern Hemisphere, officials might finally be zeroing in on concrete evidence of the plane and its fate.
A discovery of the plane using the sonic technology would be particularly extraordinary considering that the batteries in the black boxes are expected to expire as soon as this week. Once the batteries are dead, the boxes' sonic beacons will cease operating, making the discovery of undersea wreckage far more difficult.
Search forces deployed the underwater listening technology beginning only last Friday in a last-ditch effort to try to hear the black boxes' signals before they faded.
Ocean Shield is outfitted with a so-called towed pinger locator, a batwing-shaped device that is towed below the vessel and can pick up signals from the black boxes' beacons.
The Malaysia Airlines plane disappeared on March 8 with 239 people on board after it veered off its scheduled route from Kuala Lumpur to Beijing, disappearing from civilian and military radar. Based on analysis of satellite data, officials concluded that the flight ended somewhere in the southern Indian Ocean.
Further data analysis has refined the search coordinates, and in the past week and a half the search, which has included a flotilla of ships and daily reconnaissance flights by aircraft from several nations, has focused on a broad swath of the Indian Ocean hundreds of miles off the coast of Western Australia.
Despite these efforts, no confirmed debris has been found.
"I would now like to find some wreckage because that will help solve the mystery," Houston said Monday. "Fundamentally, without wreckage, we can't say it is definitely here. We have to go down and have a look."
Over the weekend, searchers' hopes had moved to a spot about 375 miles southwest of Ocean Shield, and about 1,000 miles northwest of Perth, where a Chinese ship in the search flotilla had reported capturing two signals thought to be from the flight's black boxes.
A ship from the British Navy equipped with underwater listening technology was diverted from another area in the Indian Ocean to investigate the findings of the Chinese vessel, which reported that its own underwater listening devices had picked up signals on Friday and Saturday that were consistent with the pings emitted by a plane's black boxes.
Houston said that the signals picked up by the Chinese vessel, Haixun 01, would still be pursued, adding that it was "unlikely" that they came from the same source as the signals heard by the Australian vessel.
"We have to prosecute both contacts," he said. "We don't know at the moment, we don't have any confirmation, that one or the other is significant enough for us to say, 'Yes, this is where the aircraft is.' We have to have further confirmation, and I would put it to you that we cannot confirm until we have found some wreckage."
Asked if searchers were close to finding the black boxes, Houston replied: "I think the lead we have at the moment justifies a very thorough prosecution."
The next step will be for technicians onboard the Ocean Shield to "try to fix the position" of the signal, he said, and he anticipated that the pinger locator would have to be used for at least another day and possibly several days to narrow the location further. If a small area of the seafloor can be pinpointed as promising, searchers would deploy a remote-controlled submarine to map the sea bed.
Houston said the ocean at Ocean Shield's location is about 2.8 miles deep - about the furthest the submarine can dive, he said.
If the transmissions are confirmed as having come from the plane's black boxes, he said, the depth of the ocean in that area would ensure that recovery operations take "a long, long time."
"We're talking about a long operation here which will be measured in months, and we have yet to find the aircraft," he said.
Houston also said he found it "extraordinary" that signals had been detected even though no debris from the plane had yet been found on the surface. Air crashes on water usually leave considerable floating wreckage, at least initially.
But officials continued to caution against certainty about the source of the signals, warning that false alerts could be set off by sea life - including whales - or by noise from ships, among other causes.
Earlier on Monday, the HMS Echo, a British ship that is also outfitted with underwater listening technology, had arrived at the location elsewhere in the broad search area of the Indian Ocean to investigate the reports by the Chinese ship, Haixun 01.
As many as nine military planes, three civilian planes and 14 ships were scheduled to participate in the search on Monday.