PERTH, Australia (AFP) ― Australia on Sunday sent planes and ships to investigate signals detected by a Chinese ship in the hunt for a missing Malaysian jet, saying they matched black box beacons and were an “important and encouraging lead.”

Angus Houston, the Australian head of the mission, said a second “ping” was also being scrutinized 300 nautical miles away in the Indian Ocean, as the one-month lifespan of batteries powering the beacons loomed.

He said China’s Haixun 01 has twice detected an underwater signal on a frequency used for flight data and cockpit voice recorders ― once for 90 seconds on Saturday and another more fleeting “ping” on Friday a short distance away.

“This is an important and encouraging lead but one which I urge you to continue to treat carefully, we are working in a very big ocean and within a very large search area,” Houston told reporters.

“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.”

Britain’s HMS Echo and the Australian ship Ocean Shield ― both also equipped with black box locators ― and Australian air force planes were being diverted to the area to help discount or confirm the signals, Houston said.

Ocean Shield was also investigating a 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 mission was taking both detections “very seriously” as time ticked down on the beacons’ battery life, though he described the Chinese finding as the most 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, which vanished on a flight between Kuala Lumpur and Beijing on March 8, 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 skeptical and said it was vital to find supporting evidence.

Houston said Haixun 01 was in waters about 4.5 kilometers 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.

The Malaysia Airlines mystery has been compared with Air France Flight 447, which crashed into the Atlantic in 2009. Debris was located within a week but it took two years for undersea drones to recover the black box.

Houston said that time was critical.

“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 216,000 square kilometers of the Indian Ocean around 2,000 kilometers northwest 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.

Anish Patel, president of US black box beacon manufacturer Dukane Seacom, has said he is “highly skeptical” about the Chinese report in the absence of any supporting evidence.

“Let’s get some additional assets in the water so we can corroborate, before we get everyone’s hopes up. Before we disappoint these families one more time I think we need to corroborate,” he told CNN Saturday.

But Charitha Pattiaratchi, a professor of coastal oceanography at the University of Western Australia, said the news was exciting.

“The 35.7 kHz is a man-made noise. There’s not another noise at that frequency,” he told AFP. “A whale or a dolphin or rain or an underwater earthquake ... they have a completely different frequency.”

Malaysian authorities believe satellite readings indicate MH370 crashed in the Indian Ocean after veering dramatically off course for reasons that remain unknown.

A criminal probe has focused on the possibility of a hijacking, sabotage or psychological problems among passengers or crew, but there is no evidence yet to support any of the theories.