PERTH, Australia - Australia on Sunday said it was "hopeful" about a signal detected by a Chinese ship searching for MH370, but cautioned there is no evidence yet that it emanated from the missing plane's black box.
The signal matches the frequency used by beacons attached to the flight data recorder and the cockpit voice recorder on the Malaysia Airlines Boeing 777, the manufacturers Honeywell Aerospace have said.
The search for the jet, which vanished on a flight between Kuala Lumpur and Beijing on March 8, has intensified as time runs out to find the black box, with the batteries powering the beacons nearing the end of a roughly 30-day life span.
Australian Prime Minister Tony Abbott, who is on an official visit to Japan, welcomed news of the underwater signals, but urged caution.
"We are hopeful but by no means certain. This is the most difficult search in human history, we are searching for an aircraft which is at the bottom of a very deep ocean and it's a very, very wide search area," he told reporters in Tokyo.
"While we certainly are throwing everything we have at it, and while the best brains and the best technology in the world will be deployed, we need to be very careful about coming to hard and fast conclusions too soon."
Some analysts greeted the development with optimism, saying a 37.5kHz signal can only be transmitted by an emergency beacon.
But others voiced scepticism, including doubts over why there were not two "pings" if both recorders were in the same vicinity.
White objects sighted around 90 kilometres (56 miles) from the area where the signal was detected also raised hopes, but were later reported by China's official Xinhua news agency to be floating junk unrelated to the missing plane.
Signal 'consistent with black box'
The Chinese vessel, Haixun 01, picked up the pulse signal with a black box detector during searches Saturday at about 25 degrees south latitude and 101 degrees east longitude, Xinhua said
. Air Chief Marshal Angus Houston, the Australian head of coordination in the search, said the signal's characteristics "are consistent with the aircraft black box", though he warned no link with MH370 had been verified.
Up to 10 military planes, two civil planes and 13 ships will scour the remote waters on Sunday, concentrating on about 216,000 square kilometres of the Indian Ocean around 2,000 kilometres northwest of Perth.
The Joint Agency Coordination Centre which Houston leads said Sunday that weather in the search area - which is periodically pounded with storms - was expected to be good, with visibility greater than 10 kilometres.
Note of caution
Anish Patel, president of US black box beacon manufacturer Dukane Seacom, said Saturday he was "highly sceptical" about the Chinese report.
"I would like to understand why not two signals - there should be a second beacon from either the flight data recorder or the voice recorder. So if the recorders are adjacent or within reasonable proximity... they should have detected possibly two signals," he told CNN.
"So 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."
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, adding that this was exactly why black box pingers were set at this frequency.
"A whale or a dolphin or rain or an underwater earthquake... they have a completely different frequency."
Australia has asked China for more information on the finding, Houston said, and was considering deploying search assets to the area.
Chinese officials also warned the signal had not yet been identified.
"Suspected pulse signal picked up by Haixun 01 has not been identified yet," the China Maritime Search and Rescue Center said on a verified microblog.
Australian and British vessels are also currently involved in a round-the-clock underwater search hoping to pick up a signal from the black box.
The Ocean Shield, which is carrying a US Navy black box detector, and HMS Echo, which has a similar capability, are searching a 240-kilometre track of ocean in hopes of detecting sonic pings from the recorder but progress is slow.
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.