An Australian ship searching for underwater signals from missing Malaysian Airlines plane MH370 has detected two signals, one which lasted more than two hours, Australian authorities have revealed.
Air Chief Marshall (ret) Angus Houston, the head of the Joint Agency Coordination Centre, said the Navy vessel Ocean Shield detected the signals twice in the past 24 hours.
He said the first contact lasted two hours 20 minutes and the second lasted 13 minutes.
The two distinct “pinger” returns were consistent with the flight data and cockpit voice recorders, ACM Houston said.
The Ocean Shield is scouring the area attempting to regain the signal.
ACM Houston cautioned that the signals were yet to be determined as being from MH370. He said more information was needed.
“We haven't found the aircraft yet,” he said.
The water depth in the area is 4500m.
"We cannot confirm it is from MH370 until we have found some wreckage," ACM Houston said.
"We need a good position on the ocean floor to search."
The area being searched was separate to the area in which the Chinese ship detected a signal over the weekend.
"This is a very time-intensive operation. To turn the vessel around to search again takes three hours," ACM Houston said.
"This is the most promising lead in the search so far. It is the best information we have had.
"I'm much more optimistic than I was a week ago."
As time ticked down on the battery life of the black box's tracking beacons, CNN reported overnight that the missing airliner may have flown around Indonesia airspace on the night it disappeared 'in what may have been a deliberate attempt to avoid radar detection'.
A senior Malaysian Government official reportedly told CNN that MH370 made the detour after it had left Malaysian military radar.
Up to nine military planes, three civil planes and 14 ships will assist in today's search.
The search area is expected to be approximately 234,000 square kilometres.
Good weather is expected throughout the day with showers in the afternoon although this is not expected to affect the search.
ADV Ocean Shield is continuing investigations in its own area.
HMS Echo is en-route to assist the Chinese vessel Haixun 01, which detected pulse signals in the Indian Ocean.
The Australian Transport Safety Bureau continues to refine the area where the aircraft entered the water based.
ACM Angus Houston said that China's Haixun 01 had twice detected an underwater signal on a frequency used for the plane's flight data and cockpit voice recorders -- once for 90 seconds on Saturday and another more fleeting "ping" on Friday a short distance away.
The Malaysia Airlines Boeing 777 with 239 people aboard vanished on March 8 during a flight from Kuala Lumpur to Beijing.
"This is an important and encouraging lead but one which I urge you to continue to treat carefully," Houston told reporters.
"We are working in a very big ocean and within a very large search area."
"Speculation and unconfirmed reports can see the loved ones of the passengers put through terrible stress and I don't want to put them under any further emotional distress at this very difficult time."
A spokeswoman for Britain's Ministry of Defence confirmed late Sunday that the HMS Echo, equipped with a black box locator, had arrived in the area where the Chinese had reported a ping.
"It will start its work to find the black box in the next hour," the spokeswoman told AFP.
Earlier, Houston said Australian ship Ocean Shield -- also equipped with a black box locator -- and Australian air force planes were being diverted to the area to help discount or confirm the Chinese signals.
Ocean Shield was also investigating the signal it detected on Sunday in its current location, about 300 nautical miles north of Haixun 01, in waters far off Australia's west coast.
Houston said the Chinese finding was more promising.
"I think the fact that we've had two detections, two acoustic events in that location, provides some promise which requires a full investigation," he said.
The hunt for the jet was refocused on the southern end of the search zone Sunday after corrected satellite data showed it was more likely the plane entered the water there.
Houston said the Haixun 01 was already operating in that more southerly zone.
Some analysts greeted the acoustic detections with optimism, saying a 37.5kHz signal can only be transmitted by an emergency beacon. But others were sceptical and said it was vital to find supporting evidence.
Houston said Haixun 01 was in waters about 4.5 kilometres (nearly three miles) deep, meaning "any recovery operation is going to be incredibly challenging and very demanding and will take a long period of time" if the plane is found there.
"This is Day 30 of the search and the advertised time for the life of the batteries in the beacon is 30 days. Sometimes they last for several days beyond that -- say eight to 10 days beyond that -- but we're running out of time in terms of the battery life of the emergency locator beacons."
Up to 10 military planes, two civil aircraft and 13 ships were scouring the remote waters on Sunday, concentrating on about 216,000sq km of the Indian Ocean around 2000km north-west of Perth.
Houston insisted that China was "sharing everything that's relevant to this search" with the lead authority, and sidestepped questions over the Haixun 01's location far from the other lead vessels in the search.
"China has seven ships out there, that's by far the largest fleet of ships out there. I think we should be focusing on the positives," he said.