Ships and planes pursued Saturday the search for the missing Malaysian airliner off Australia after Prime Minister Tony Abbott said he was "very confident" that signals from the black box had been detected.
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.
The Joint Agency coordination Centre (JACC) said Saturday that the remote search area where the plane was believed to have gone down some was still shrinking.
"Today, 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," JACC said.
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 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 adding that there have been no confirmed signal detections over the past 24 hours.
On a trip to China, home to two-thirds of the 239 people on board MH370, Abbott suggested the plane might soon be found.
"We have very much narrowed down the search area and we are very confident the signals are from the black box," Abbott said, while warning that the transmissions were "starting to fade".
Abbott was speaking in Shanghai before meeting Chinese President Xi Jinping at the Great Hall of the People in Beijing.
"We are confident that we know the position of the black box flight recorder to within some kilometres," Abbott said.
But he warned much remained to be done in "recovering wreckage from almost 4.5 kilometres beneath the sea, or finally determining all that happened on that flight".
The cause of the plane's diversion remains unknown.
After Abbott spoke, search chief Angus Houston struck a much more cautious note saying "there has been no major breakthrough in the search for MH370".
He said the Ocean Shield would continue to trawl for pings.
"It is vital to glean as much information as possible while the batteries on the underwater locator beacons may still be active," said Houston, head of the Perth-based JACC that is organising the challenging search.
A decision to deploy a submersible sonar device "could be some days away", he said.
Still no debris found
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, with the weather forecast for isolated showers and sea swells up to one metre, with visibility of five kilometres during showers.
Houston has stressed the need to find the wreckage to be absolutely certain of the plane's fate, and has repeatedly warned against unduly inflating hopes for the sake of victims' relatives, whose month-long nightmare has been punctuated by false leads.
Frustrated Chinese relatives have accused the Malaysian flag carrier of bungling the response to the plane's disappearance and withholding information, which Malaysia's government denies.
The rancour has strained ties between Malaysia and China, whose government also has put pressure on authorities in Kuala Lumpur.
Malaysia's environment minister told AFP Friday that China had postponed plans to send a pair of pandas to Malaysia next week.
China had agreed in 2010 to lend the two giant pandas for 10 years in Beijing's latest use of "panda diplomacy" to cement ties with other countries.