"Given that the signal from the black box is rapidly fading, what we are now doing is trying to get as many detections as we can so that we can narrow the search area down to as small an area as possible," Abbott said.
"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," he said in Beijing on the last day of his China visit.
Abbott said a submersible drone would be sent to conduct a sonar search of the seabed once search teams were confident with the area identified - but he refused to say when that might be.
"We do have a high degree of confidence the transmissions we have been picking up are from flight MH370," Abbott said, adding that "no one should under-estimate the difficulties of the task ahead of us."
Abbott appeared to be taking a cautious approach after voicing confidence yesterday that signals from the black box had been detected which triggered speculation that a breakthrough was imminent.
Angus Houston, the Head of the agency coordinating the search, had sounded a note of caution yesterday itself, saying there had been "no major breakthrough".
The Beijing-bound Malaysia Airlines flight MH370 - carrying 239 people, including five Indians, an Indo-Canadian and 154 Chinese nationals - had mysteriously vanished on March 8 after taking off from Kuala Lumpur.
Meanwhile, a media report today said the co-pilot of missing plane made a desperate call from his mobile phone moments before the jet went off the radar.
The call from co-pilot Fariq Abdul Hamid's phone, however, ended abruptly, but not before contact was established with a telecommunications sub-station in Penang state, the New Straits Times reported.
The call was made as the jet was flying low near Penang island on Malaysia's west coast, the morning it went missing.
The telco's (telecommunications company's) tower established the call that he was trying to make. On why the call was cut off, it was likely because the aircraft was fast
moving away from the tower and had not come under the coverage of the next one," the New Straits Times said, citing unnamed sources.
The paper said it was unable to ascertain who Fariq was trying to call as sources chose not to divulge details of theinvestigation. The links that police are trying to establish are also unclear, the report said.
Investigators are poring over this discovery as they try to piece together what had happened moments before the Boeing 777 Flight MH370 went off the radar, some 200 nautical miles northwest of Penang, the paper said.
Fariq's last communication through the WhatsApp Messenger application was about 11.30pm on March 7, just before he boarded the jet for his six-hour flight to Beijing.
The paper said checks on Fariq's phone history showed the last person he spoke to was "one of his regular contacts (a number that frequently appears on his outgoing phone logs)".
This call was made no more than two hours before the flight took off from Kuala Lumpur International Airport.
Citing sources close to the investigations, the paper said that checks on Fariq's phone showed that connection to the phone had been "detached" before the plane took off.
On today's operations, the Joint Agency Coordination Centre (JACC) said: "Australian defence vessel Ocean Shield continues more focused sweeps with the towed pinger locater to try and locate further signals related to the aircraft's black
The Australian ship has picked up four signals linked to aircraft black boxes, with the first two analysed as being consistent with those from aircraft flight recorders.
Finding the black box is crucial for knowing what happened on March 8 when the plane disappeared under mysterious circumstances.
The batteries powering the black box are certified to be working for 30 days. Stored in a plane's tail, they are designed to begin sending off distinct, high-pitched pings or
signals as soon as they come in contact with water.
Today's total search covered 41,393 square kilometres and the core of the search zone was 2,330 kilometres northwest of Perth.
"This work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed," the JACC said.