International rescue teams searching for missing flight MH370 believe they may have detected the plane’s black box flight recorders after a ship picked up signals in the southern Indian Ocean.

The Australian defence vessel Ocean Shield picked up signals twice, around 370 miles north of where two signals were detected by a Chinese ship on Saturday.

Crucially, there were two distinct pinger returns – suggesting transmissions from a flight data recorder and cockpit voice recorder on a Boeing 777 jet.

Angus Houston, the former Australian defence chief heading the search, said the information was “the most promising lead” in the search so far.

But he warned it could be days before authorities confirm if the signals are from the Malaysia Airlines flight, which vanished on March 8 with 239 people on board.

Malaysian acting Transport Minister Hishammuddin Hussein said he was “cautiously hopeful that there will be a positive development in the next few days, if not hours”.

Search teams are involved in a race against time as the batteries on the plane’s flight recorders could run out at any moment, meaning the signals would no longer be emitted.

Mr Houston said the Ocean Shield detected the sounds on two occasions over a period totalling more than two-and-a-half hours.

He said: “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.

“This would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder.”

Stressing the need for further confirmation, he said: “I am much more optimistic than I was a week ago.”

But he added: “We are talking about a long operation here and we have yet to find the aircraft.”

Search co-ordinators stressed the signals were picked up in very deep water – 4,500 metres – which is at the limit of underwater search equipment being used.

The position of the sound needed to be further pinpointed, and then an underwater drone could be sent down to investigate, Mr Houston said.

He went on: “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.

“I would want more confirmation before we say this is it. 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.”

The latest development in the search effort came as the British navy ship HMS Echo joined the hunt. The vessel carries sophisticated sound-locating equipment.

No wreckage from the plane has been found during the month-long search, despite a number of debris sightings.

Malaysian officials concluded – based on satellite data from several countries – that the aircraft crashed into the southern Indian Ocean to the west of Perth.

Investigators have not established why the plane lost contact with air traffic controllers and appeared to divert so far from its intended route from Kuala Lumpur to Beijing.

The backgrounds of passengers, crew and both pilots have been investigated, while terrorism and hijack have also been considered as possible explanations for the plane’s disappearance.

The families of those on board have been frustrated by the huge international search operation, accusing the Malaysian authorities of mismanagement and holding back information.

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