After weeks of searching vast swaths of ocean, investigators now have their "most promising" lead yet in efforts to find Malaysia Airlines Flight 370.
A pinger locator in the Indian Ocean has detected signals consistent with those sent by a flight data recorder and a cockpit voice recorder, said the head of the Australian agency coordinating search operations.
The signals were picked up Sunday by the Ocean Shield, an Australian navy ship that's towing a sophisticated U.S. pinger locator through an area about 1,750 kilometers (1,100 miles) northwest of Perth. The first detection lasted for more than two hours; a second lasted for about 13 minutes.
The sounds were heard in a part of the ocean that's about 4,500 meters (about 14,800 feet) deep, retired Air Chief Marshal Angus Houston said Monday.
"We've got a visual indication on a screen, and we've also got an audible signal. And the audible signal sounds to me just like an emergency locator beacon," he said.
"We are encouraged that we are very close to where we need to be."
But it could take days before officials can confirm whether the signals came from the plane, which fell off radar on March 8 with 239 people on board.
"In very deep oceanic water, nothing happens fast," Houston said. "I would ask all of you to treat this information cautiously and responsibly. ... We haven't found the aircraft yet."
"We have a promising lead, but we have yet to get confirming evidence."
At least one investigator has described the search not as finding a needle in a haystack, but rather trying to find the haystack.
"It's very exciting, very exciting," forensic audio expert Paul Ginsberg said Monday. "I think we have finally found the haystack."
And Malaysian authorities are hopeful there will be a positive development in the next few days, if not hours, acting Transportation Minister Hishammuddin Hussein told reporters Monday.
But some friends and relatives of passengers said they're not putting too much stock in Monday's news.
"Until they physically locate the bulk of the plane with the black box intact and passenger bodies, I won't believe it," said Sarah Bajc, the partner of American passenger Philip Wood.
Teams are also still investigating pings detected Friday and Saturday by a Chinese ship about 600 kilometers (375 miles) southwest of the area that the Ocean Shield is searching.
But time could be running out in tracing the sounds. In a few hours or days, the pingers aboard the plane could stop transmitting for good.
The batteries inside the beacons, which are designed to start sending signals when a plane crashes into water, last about 30 days after the devices are activated.
Monday marks the 31st day of the search.