Three separate electronic signals have been detected in the hunt for the black box from the missing Malaysia Airlines jet, Flight MH370.
A Chinese ship detected a pulse signal for a second time after hearing it earlier on Saturday.
Investigators have warned the signals are yet to be confirmed as coming from a black box recorder and should not be treated as such "until such time as we can provide an unequivocal determination".
Story continues after slideshow...
Search For MH370
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Open Image ModalA Chinese relative of passengers on the missing Malaysia Airlines flight MH370 uses a lighter as she prays at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO/WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalChinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalChinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalA woman reacts as Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalChinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalA woman lights a candle as Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalPERTH, AUSTRALIA - APRIL 08: Air Chief Marshal Angus Houston (Ret'd) and Defence Minister David Johnston address the media during a press conference over the continuing search for missing Malaysia Airlines Flight MH370 at RAAF Base Pearce on April 8, 2014 in Perth, Australia. ACM Angus Houston advised the towed pinger by ADV Ocean Shield is still trying to re-locate the signals previously detected, which were believed to be consistent with aircraft black boxes. The airliner disappeared on March 8 with 239 passengers and crew on board and is suspected to have crashed into the southern Indian Ocean. (Photo by Paul Kane/Getty Images) (credit:Getty Images)
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Open Image ModalPERTH, AUSTRALIA - APRIL 07: A US Navy Poseidon P-8 takes off to assist in the search for debris from missing Malaysia Airlines Flight MH370 at Perth International airport on April 7, 2014 in Perth, Australia. Angus Houston confirmed today that the Australian naval vessel Ocean Shield has twice detected signals in the past 24 hours consitent with aircraft black boxes. The airliner disappeared on March 8 with 239 passengers and crew on board and is suspected to have crashed into the southern Indian Ocean. (Photo by Paul Kane/Getty Images) (credit:Getty Images)
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Open Image ModalAngus Houston, head of the Joint Agency Coordination Centre leading the search for missing Malaysia Airlines flight MH370, points to a graphic of the search area during a media conference in Perth on April 7, 2014. An Australian navy ship has detected new underwater signals consistent with aircraft black boxes, Houston said on April 7, describing it as the 'most promising lead' so far in the month-old hunt for missing Flight MH370. AFP PHOTO / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalPERTH, AUSTRALIA - APRIL 07: Air Chief Marshal Angus Houston (ret'd) holds a map outlining the current search areas of naval ships Ocean Shield and Haixun 01 during a press conference for the continuing search of missing Malaysia Airlines Flight MH370 at Dumas House on April 7, 2014 in Perth, Australia. Angus Houston confirmed today that the Australian naval vessel Ocean Shield has twice detected signals in the past 24 hours consitent with aircraft black boxes. The airliner disappeared on March 8 with 239 passengers and crew on board and is suspected to have crashed into the southern Indian Ocean. (Photo by Paul Kane/Getty Images) (credit:Getty Images)
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Open Image ModalMalaysian Buddhists offer prayers for passengers onboard missing Malaysia Airlines (MAS) flight MH370 in Kuala Lumpur on April 6, 2014. A Chinese ship searching the Indian Ocean for flight MH370 detected a signal at a frequency used by the missing aircraft's black boxes on April 5, but Australia warned there was no evidence yet that it was linked to the plane. AFP PHOTO / MOHD RASFAN (Photo credit should read MOHD RASFAN/AFP/Getty Images) (credit:Getty Images)
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Open Image ModalAn Australian Air Force Orion takes off from Pearce Airbase in Bullsbrook, 35 km north of Perth, to join the hunt for a missing Malaysia Airlines plane in the Indian Ocean on April 6, 2014. Planes and ships were being diverted on April 6 to the area where a Chinese vessel detected signals consistent with a black box beacon in the hunt for missing Malaysia Airlines flight MH370, the search chief said. AFP PHOTO / Tony ASHBY (Photo credit should read TONY ASHBY/AFP/Getty Images) (credit:Getty Images)
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The latest signal was found in a different area being searched by international teams. It is around 220 miles south of the closest of the three areas searched.
A British naval ship, HMS Echo, is heading to the are to help with the search.
The signal had a very specific frequency, 37.5 kilohertz (cycles per second). It is chosen as a signal for a black box because it stands out from other frequencies. Nothing else that lives in the sea could naturally make that sound.
“I have been advised that a series of sounds have been detected by a Chinese ship in the search area," said the Australian Chief Coordinator of the Joint Agency Coordination Centre, Air Chief Marshal Angus Houston.
"The characteristics reported are consistent with the aircraft black box. A number of white objects were also sighted on the surface about 90 kilometres from the detection area.
"We are working in a very big ocean and within a very large search area, and so far since the aircraft went missing we have had very few leads which allow us to narrow the search area.
"I assure you that we will follow up and exhaust every credible lead that we receive."
Malaysia's civil aviation chief, Azharuddin Abdul Rahman, confirmed that the frequency emitted by MH370's black box was 37.5 kilohertz and said authorities were trying to verify the report.
The reporter, speaking to Chinese broadcaster CCTV, said the signal was first detected on Friday, intermittently for about 15 minutes. But then it was detected again Saturday morning, every second for 90 seconds.
The area where the supposed pulse was detected is an underwater mountain range similar to the Usambara mountains, up to 8,200 feet in depth.
Australian Defence Minister David Johnston had earlier urged caution. "This is not the first time we have had something that has turned out to be very disappointing," he told ABC television.
The longer the black box flight recorder remains unfound, the shorter the window of time investigators are working with.
With the battery due to run out on Monday or Tuesday next week, the likelihood that the device will be found is declining rapidly.
Ships have sighted a number of objects in the massive search area, but none have been associated with the missing plane.
If the black box's battery runs out before searchers locate it, the device could not be found for years.