SYDNEY, (AFP) - The search for missing Malaysia Airlines Flight MH370 will likely continue for "a long time", Australian Prime Minister Tony Abbott warned Saturday, a day after voicing confidence 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.

"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 "no one should under-estimate the difficulties of the task ahead of us," he added in a press conference broadcast live on Sky television.

"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," Abbott said.

His comments come a day after he said he was "very confident" that signals detected in the search for Flight MH370 are from the aircraft's black box, whose batteries are waning fast more than a month after the plane vanished.

Four signals linked to aircraft beacons have been detected by the Australian vessel Ocean Shield using US equipment, with the first two analysed as being consistent with those from aircraft flight recorders.

"We are confident that we know the position of the black box flight recorder to  within some kilometres," Abbott said Friday on his trip to China, home to two-thirds of the 239 people on board the plane.

However, search chief Angus Houston struck a much more cautious note saying "there has been no major breakthrough in the search for MH370".

The Perth-based Joint Agency coordination Centre (JACC) said Saturday that the remote search area where the plane was believed to have gone down was still shrinking.

Up to 10 aircraft and 14 ships were taking part in the hunt on Saturday.