(Corrects search depth to 4.5 km in paragraph 9, fixes typographical errors in paragraphs 4, 6)
By Jane Wardell
SYDNEY, April 7 (Reuters) - Australian officials said on Monday signals picked up by a black box detector attached to an Australian ship searching for missing Malaysia Airlines Flight MH370 in the Indian Ocean were consistent with aircraft flight recorders.
"Clearly, this is a most promising lead," Angus Houston, head of the Australian agency coordinating the search, told a news conference in Perth in western Australia.
Houston, a retired air chief marshal, said two signals had been detected off Australia's northwest coast.
The first detection held for 2.5 hours before the ship lost contact. After turning around, the ship picked up the signal for around 13 minutes, he said.
"On this occasion two distinct pinger returns were audible," Houston said. "Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder."
Confirmation of whether the signals were emitted from the Kuala Lumpur-to-Beijing bound plane, missing since March 8 with 239 people on board, could take several days, Houston said.
The black boxes, thought be to lying on the ocean floor, are equipped with locator beacons that send pings but the beacons' batteries are thought to be running out of charge by now, a month after Flight MH370 disappeared.
The U.S. Navy "pinger locator" connected to the Australian ship Ocean Shield was trawling an area some 300 nautical miles away from separate reports by Chinese patrol ship Haixun 01 of a pulse signal with the same frequency of a black box.
If the signals can be narrowed further, an unmanned underwater vehicle, Bluefin 21, will be sent to attempt to locate wreckage on the sea floor to verify the signals, said Houston, who noted that the potential search area was 4.5 km (2.8 miles) deep, the same as the Bluefin range.
"We are right on the edge of capability and we might be limited on capability if the aircraft ended up in deeper water," he said. "In very deep oceanic water, nothing happens fast."
He said that while Ocean Shield continued to trawl the area to try to regain contact, search teams were also investigating the reports by the Chinese ship several hundred kilometres away. (Reporting By Jane Wardell; Editing by Paul Tait and Michael Perry)