International search planes and ships are heading to an area where a Chinese ship twice heard what could be signals from missing Malaysia Airlines Flight MH370’s black box locators, Australian search authorities said on Sunday.
Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, told a media conference in Perth that two reported acoustic detections from the Haixun 01 were a good lead but there remained no certainty that they had come from the missing plane.
Aircrews from seven countries have been flying dozens of missions from Perth deep into the southern Indian Ocean looking for debris from the jet and have been joined by ships fitted with sophisticated equipment designed to pick up the locators on the black box voice and data recorders.
The Boeing 777 lost communications and disappeared from civilian radar less than an hour into an overnight flight from Kuala Lumpur to Beijing on March 8.
A black box detector deployed by Haixun 01 picked up a pulse signal of 37.5 kHz per second at around 25 degrees south latitude and 101 degrees east longitude, Xinhua reported.
Australian ship 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.
Chinese search planes also reported spotting white objects in the ocean.
Houston said: "White objects were sighted on the surface about 90 kilometres from the detection area.
View MH370: possible locations  in a larger map
"However, there is no confirmation at this stage that the signals and the objects are related to the missing aircraft."
The underwater locator beacon on the black box of a Boeing 777 can transmit an ultrasonic pulse from as deep as 4.3 kilometres under water.
But the signal will be silenced when the battery runs out - usually after about 30 days.
As many as 13 planes and 11 ships are involved in the hunt for MH370 - which vanished on March 8 with 239 people on board - in an area 1,700 kilometres northwest of Perth.
Li Jie, a researcher at the PLA Navy's Military Academy, said the detection was an important breakthrough. "Only the black box will release such a pulse signal," he said.
Rear Admiral Yin Zhuo told state-run CCTV that it was highly likely the signal was from the black box of MH370.
"The area is not a major route for commercial jets and vessels, and therefore the chance that the signal is from another crashed airliner is minimal," he said.
But Australian Defence Minister David Johnston urged caution after several false leads in what has been an "emotional roller coaster" for the families of those on board the plane.
He said: "This is not the first time we've had something that has turned out to be very disappointing. There's a huge chance of a false positive here."
Watch: How does a 'black box' work?
The Chinese Maritime Rescue Centre also warned there was no confirmed link between the pulse signal and the missing plane.
Chris Yates, an aviation security consultant based in Britain, warned that the black box would now be in a "rundown state" with its battery being exhausted.
"The range of the transmission from the black box will have decreased significantly over such a period of time," he said.
"That will cast doubts on the veracity of the claimed findings."
He added that the position where the signals were detected seemed to be further north than the current search area.
In Beijing, relatives of passengers on the flight said they did not believe the pulse signal was from the plane. One said: "We should rather wait for official confirmation than listen to unconfirmed sources of information."
Another family member said: "I just hope this is not true. I won't believe it until they have found the wreckage and bodies."
Haixun 01 was one of the first batch of Chinese vessels sent to help in the search for MH370.
It is the largest and most advanced China-produced patrol and rescue vessel and arrived in the southern Indian Ocean on March 20.
Additional reporting by Minnie Chan and Shirley Zhao