An Australian aircraft hunting for the missing Malaysian jet picked up a new possible underwater signal on Thursday in the same area search crews previously detected sounds that were consistent with an aircraft's black boxes.

The Australian navy P-3 Orion, which has been dropping sound-locating buoys into the water near where the original sounds were heard, picked up a "possible signal" that may be from a man-made source, said Angus Houston, who is coordinating the search off Australia's west coast.

A hunt for debris on the ocean surface intensified Thursday, with the search zone narrowed to its smallest size yet — 57,900 square kilometers (22,300 square miles), or about one-quarter the size it was a few days ago. Fourteen planes and 13 ships were taking part in the hunt for floating debris, about 2,300 kilometers (1,400 miles) northwest of Perth.

A "large number of objects" had been spotted by crews combing the area for floating debris on Wednesday, but the few that had been retrieved by search vessels were not believed to be related to the missing plane, the search coordination center said.

Houston has expressed optimism about the sounds detected earlier in the week, saying on Wednesday that he was hopeful crews would find the aircraft — or what's left of it — in the "not-too-distant future."

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