Angus Houston, the head of a joint agency coordinating the search in the southern Indian Ocean, called it "very encouraging" but said it may take days to confirm whether signals picked up by the ship Ocean Shield are indeed from the flight recorders on Flight 370.
The Australian navy ship Ocean Shield, using a U.S. Navy towed pinger locator, detected the sounds on two occasions over a period totaling more than two and a half hours.
"Clearly this is a most promising lead, and probably in the search so far, it's the probably the best information that we have had," Houston said at a news conference.
"This would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," he said.
He said the position of the noise needs to be further refined, and then an underwater autonomous vehicle can be sent in to investigate.
"It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370. In very deep oceanic water, nothing happens fast."
The plane vanished March 8 during a flight from Kuala Lumpur, Malaysia, to Beijing with 239 people on board, setting off an international search that started off Vietnam and then shifted to the southern Indian Ocean as information from radar and satellite data was refined.
The length of the search and lack of any information on the cause of the plane to go so far off course has transfixed the world, and made finding the black boxes important to finding a possible cause.
Houston said the Ocean Shield detected two separate signal detections in the northern part of the defined search area, with the first detected for approximately two hours and 20 minutes, and the second for 13 minutes on the ship's return trip over the same area.
He said the depth in the area is approximately 4,500 meters (14,800 feet), and he cautioned that it was too early to say the transmissions were coming from the black boxes on the missing passenger jet.
"I would want more confirmation before we say this is it," he said. "Without wreckage, we can't say it's definitely here. We've got to go down and have a look and hopefully we'll find it somewhere in the area that we narrowed to."
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