SYDNEY — China, Japan, and Britain have joined the search for signs of the missing Malaysia Airlines airliner far off Australia’s west coast, where Australian aircraft are scanning a remote expanse of ocean for floating debris that might be wreckage from the airliner.
Three Australian planes took off at dawn Saturday for a third day of scouring the region about 1,500 miles southwest of Perth, the Associated Press reported
A total of six Australian aircraft were to search the region Saturday: two ultralong-range commercial jets and four P-3 Orions, the Australian Maritime Safety Authority said.
Two merchant ships were in the area, and the HMAS Success, an Australian Navy supply ship, was due to arrive late Saturday afternoon. Weather in the search zone was relatively good.
A satellite spotted two large objects in the area earlier this week, raising hopes of finding the Boeing 777 that disappeared March 8 with 239 people on board. Human spotters were unable to confirm the finding in the first two days of searching.
The expansion of the multinational operation in the southern Indian Ocean illustrated how the bleak search for the missing jet has partly dampened regional tensions. China and Japan are locked in a dispute over islands in the East China Sea but their forces will work in coordination with the US and Australian militaries.
Almost two weeks after the plane vanished, Hishammuddin Hussein, the defense minister of Malaysia, which is in charge of the overall search, said it was “very, very” difficult to talk with waiting families about the possibility that the 227 passengers and 12 crew members had died.
Their most important question, “where are their loved ones?” cannot be answered, he said at a news conference Friday near Kuala Lumpur International Airport, where the plane left on a flight to Beijing
After the satellite images were reported, Australian Prime Minister Tony Abbott kindled hope that the waters off Western Australia might hold clues to the plane’s fate, but he tried to tamp down unrealistic expectations on Friday.
‘‘It’s about the most inaccessible spot that you could imagine on the face of the earth, but if there is anything down there, we will find it,’’ Abbott said.
Australian aircraft searched the remote expanse of ocean more than 9,800 feet deep on Friday. Although they did not find anything, Hishammuddin, who is also Malaysia’s acting transport minister, called the indistinct satellite images of the objects the best lead available and announced that more ships and surveillance planes would head to the area to help.
Japan will send two P-3 Orion surveillance aircraft to join the search, and Britain has agreed to send a naval ship, the HMS Echo, Hishammuddin said.
Separately, the Chinese government announced it would send three military aircraft to Australia for the search, joining a Chinese polar exploration vessel and merchant ships.
“This crisis has put a heavy burden on Asian countries to cooperate,” said Bridget Welsh, a political scientist at Singapore Management University. “But there’s still the issues of wariness and lack of trust between them and some other partners.”
She continued: “We see this affecting the questions of sharing data from satellite technology, working together, especially between China and the United States.”
Hishammuddin said he planned to call US Defense Secretary Chuck Hagel, to seek more “help with the search and rescue efforts, including remotely operated vehicles for deep-ocean salvage.”
But the search for signs of Flight 370 is not all high-tech. John Young, the Australian official directing the search in the southern Indian Ocean, said the Australian planes would, for now at least, abandon radar scanning and rely on human spotters. Young said that using human spotters might be slower, but that it was more promising than radar.
“Noting that we got no radar detections yesterday, we have replanned the search to be visual,” he said in a question-and-answer video posted online by the Australian Maritime Safety Authority in Canberra, the capital, where Young is general manager of the emergency response division.
The change, Young said, involved “aircraft flying relatively low, very highly skilled and trained observers looking out of the aircraft windows.”
Because of the distance from the shore, Australia’s P-3 Orions have only a couple of hours over the area where the objects may be floating, the maritime safety authority said.
“The aircraft are spaced more closely together and we will need more aircraft for a search of that type,” Young said. “Although this search area is much smaller than we started with, it nonetheless is a big area when you’re looking out the window and trying to see something by eye. We may have to do this a few times to be confident about the coverage of that search area.”
The search planes flying out to sea from a base near Perth from the international search team have included Orion P-3 surveillance aircraft, ultralong-range jets, and a US Navy P-8A Poseidon search plane.
Commander William J. Marks, the spokesman for the US Navy’s 7th Fleet, said the P-8A Poseidon would continue to use radar and other electronic sensing devices for the search. The Pentagon said it has spent $2.5 million to operate ships and aircraft in the search and has budgeted another $1.5 million for the efforts.
Hussein thanked the more than two dozen countries involved in the overall search that stretches from Kazakhstan in Central Asia to the southern Indian Ocean.
He called the whole process ‘‘a long haul.’’
Malaysian authorities have not ruled out any possible explanation for what happened to the jet but have said the evidence so far suggests it was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled.
Police are considering the possibilities of hijacking, sabotage, terrorism, or issues related to the mental health of the pilots or anyone else on board.