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.

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 the most upbeat official assessment so far when he had hinted Friday that a breakthrough was imminent.

When the prime minister announced from Shanghai that he would say no more of his "high confidence" before talking to the Chinese leadership, speculation swirled through the media 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 difficulties remaining.

"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.

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.