Perth (Australia) (AFP) - There was no let-up in the air and sea search for the missing Malaysian airliner off Australia on Saturday as Prime Minister Tony Abbott warned that locating Flight MH370 would still likely take a long time.
Abbott appeared to step back from his comments Friday when he voiced great confidence that signals from the black box had been detected -- his most upbeat assessment so far that triggered speculation that a breakthrough was imminent.
Retired air chief marshal Angus Houston who heads the hunt from Perth, had quickly issued a statement clarifying that there had been no breakthrough.
On Saturday, Abbott repeated his confidence in the search, but put the accent on the challenges ahead.
"We do have a high degree of confidence the transmissions we have been picking up are from flight MH370," Abbott said on the last day of his visit to China.
But he added, "no one should under-estimate the difficulties of the task ahead of us.
"Yes we have very considerably narrowed down the search area but trying to locate anything 4.5 kilometres beneath the surface of the ocean about a thousand kilometres from land is a massive, massive task and it is likely to continue for a long time to come."
The Australian-led search for the Boeing 777, which disappeared en route from Kuala Lumpur to Beijing, is racing to gather as many signals as possible to determine an exact resting place before a submersible is sent down to find wreckage.
On Saturday's operations, the Joint Agency Coordination Centre (JACC) said: "Australian defence vessel Ocean Shield continues more focused sweeps with the towed pinger locator to try and locate further signals related to the aircraft's black boxes."
- 'No major breakthrough' -
Ocean Shield has picked up four signals linked to aircraft black boxes, with the first two analysed as being consistent with those from aircraft flight recorders.
The beacons on the plane's flight data and cockpit voice recorders have a normal battery lifespan of around 30 days. MH370 vanished on March 8.
AP-3C Orion surveillance aircraft were also carrying out acoustic searches in conjunction with Ocean Shield, the statement said, adding that the British oceanographic ship HMS Echo was also working in the area.
Saturday's total search zone covers 41,393 square kilometres (15,982 square miles) and the core of the search zone lies 2,330 kilometres (1,450 miles) northwest of Perth.
"This work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed," JACC said.
In Kuala Lumpur, a report citing unnamed investigators said MH370's co-pilot had tried to make a mid-flight call from his mobile phone just before the plane vanished.
The call ended abruptly possibly "because the aircraft was fast moving away from the (telecommunications) tower", The New Straits Times quoted a source as saying.
But the daily also quoted another source saying that while Fariq Abdul Hamid's "line was reattached", there was no certainty that a call was made.
The story -- headlined a "desperate call for help" -- did not say who he was trying to contact.
Fariq and Captain Zaharie Ahmad Shah have come under intense scrutiny after the plane mysteriously disappeared.
Investigators last month indicated that the flight was deliberately diverted and its communication systems manually switched off as it was leaving Malaysian airspace, triggering a police investigation that has revealed little so far.
The fate of flight MH370 has been shrouded in mystery, with a number of theories put forward including a hijacking or terrorist attack and a pilot gone rogue.
There have been unconfirmed reports in the Malaysian media of calls by the captain before or during the flight.
Speaking on Friday in China, home to two-thirds of the 239 people on board the flight, Abbott suggested the mystery might soon be solved.
"We have very much narrowed down the search area and we are very confident the signals are from the black box," Abbott said, although the transmissions were "starting to fade".
"We are confident that we know the position of the black box flight recorder to within some kilometres," Abbott had said.
Abbott later met Chinese President Xi Jinping at the Great Hall of the People in Beijing.
Houston struck a much more cautious note just afterwards, saying "there has been no major breakthrough in the search for MH370".
Abbott said that he hoped to update Xi on MH370 developments again before leaving China later Saturday.
No floating debris from the plane has yet been found, the JACC said again on Saturday, despite three weeks of searching in the area by ships and planes from several countries.
Up to 10 aircraft and 14 ships were taking part in the hunt on Saturday.
Houston has stressed the need to find the wreckage to be certain of the plane's fate, and has repeatedly warned against raising hopes for the sake of victims' relatives, whose month-long nightmare has been punctuated by false leads. updates dan source HERE