(CNN) -- Australia's Prime Minister repeated Saturday that he has a "high degree of confidence" that acoustic signals detected in the Indian Ocean are from at least one of the two black boxes from the missing Malaysian plane, but predicted that finding them remains a "massive, massive task."
"It is likely to continue for a long time to come," Tony Abbott told journalists in Beijing, where he was on a diplomatic visit.
Chinese officials appreciate Australia's "transparency and candor" in the search for Malaysia Airlines Flight 370, he said, adding "I think it's to our country's credit that we've approached it that way."
More than 35 days since the plane vanished from radar screens early March 8 during a flight from Kuala Lumpur, Malaysia, to Beijing, the search continued.
Up to 11 military aircraft, one civil aircraft and 14 ships will assist in Sunday's search for the missing airliner, the Australia's Joint Agency Coordination Centre said. The Australian Maritime Safety Authority planned a visual search area totaling approximately 22,203 square miles (57,506 square kilometers). The center of the search area lies about 1,367 miles (2,200 kilometers) northwest of Perth.
During Friday's search, only a small number of the objects sighted from aircraft and ships were recovered; as has been the case throughout the effort, none was linked to the Boeing aircraft, according to the Joint Agency Coordination Centre.
Still, the U.S. Navy commander leading the American effort to find Malaysia Airlines Flight 370 said he was "optimistic" about how the search is proceeding.
The four pings detected in recent days were continuous and consistent with what a black box would emit, said Cmdr. William Marks. "We've ruled out that it was anything natural, or anything from commercial shipping, or anything like that."
"I agree with the Prime Minister," Marks said. "We're optimistic."
But the optimism was not universal.
Relatives of the 239 people who were aboard the plane when it vanished met Friday with Malaysia Airlines and government officials.
The mother of Pouria Nourmohammadi, the 19-year-old Iranian man who used a fake passport to board the plane, came away unimpressed. "I feel the Malaysian government has forgotten about all things MH370," his mother told CNN on Saturday. "These days there is not news. They only keep saying, 'We are searching.'"
On Saturday, searchers aboard the Australian vessel Ocean Shield were planning to continue towing the ping locator -- referred to as a TPL -- at a walking pace through the water in hopes of picking up new signals from either or both of the locator signals that were attached to the plane's cockpit voice recorder and flight data recorder, Marks said.
The more signals they can locate, the more investigators say they can narrow the search zone. "We have to stick with the TPL for just a little while longer to make sure we have exhausted every ounce of power coming from the battery through the black boxes," he said. The batteries were certified to last 30 days, but the beacon manufacturer predicted they would last days longer.
Once the searchers have concluded that there is no hope that the batteries could still be powering the beacons, searchers will lower into the water the Bluefin-21, a sonar device, to scour the ocean floor.
The Bluefin's pace is slower than that of the TPL, he said.
Four pings, one dud
On April 5, the TPL detected two sets of underwater pulses of a frequency close to that used by the locator beacons. Three days later, last Tuesday, it reacquired the signals twice.
All four signals were within 17 miles of one another.
A fifth ping, detected Thursday by a sonobuoy dropped from an airplane, is "unlikely to be related to the aircraft black boxes," Australian chief search coordinator Angus Houston said a day later.
Tracking pings is only one early step in the hunt to find the plane's data recorders, wreckage and the people aboard.
CNN's Ralph Ellis, David Molko and Elizabeth Joseph and journalists Ivy Sam and Chan Kok Leong contributed to this report.