The object, which appeared to be 22 meters (72 feet) by 13 meters (43 feet), was captured by satellite on Tuesday in a location that falls within the search zone that planes and ships have been crisscrossing since similar images from another satellite emerged earlier in the week. But officials have found no trace of it.
Australian Maritime Safety Authority spokeswoman Andrea Hayward-Maher said she did not know whether the precise coordinates of the location had been searched, but said officials would use the information to refine the search area on Sunday.
The maritime authority, which is overseeing the search in the region, said a civil aircraft reported seeing a number of small objects in the 36,000-square-kilometer (14,000-square-mile) area on Saturday, including a wooden pallet, but a New Zealand military plane diverted to the location found only clumps of seaweed. The agency said in a statement that searchers would keep trying to determine whether the objects are related to the lost plane.
Despite the frustrating lack of answers, Australian Prime Minister Tony Abbott on Sunday suggested the sightings were a positive development.
"Obviously we have now had a number of very credible leads and there is increasing hope - no more than hope, no more than hope - that we might be on the road to discovering what did happen to this ill-fated aircraft," Abbott told reporters in Papua New Guinea.
Three planes left a base near Perth in western Australia early Sunday to make the four-hour journey out to the search region, Hayward-Maher said. A total of eight aircraft will be involved Sunday, along with the HMAS Success, an Australian navy supply ship, she said.A cold front was forecast to move through the region later Sunday, which could bring clouds and wind, further
hampering efforts to locate the plane.
The latest satellite image is another clue in the baffling search for Malaysia Airlines Flight 370, which dropped off air traffic control screens March 8 over the Gulf of Thailand with 239 people on board.
After about a week of confusion, Malaysian authorities said pings sent by the Boeing 777-200 for several hours after it disappeared indicated that the plane ended up in one of two huge arcs: a northern corridor stretching from Malaysia to Central Asia, or a southern corridor that stretches toward Antarctica.
The discovery of the initial two objects by a satellite led several countries to send planes and ships to a stretch of the Indian Ocean about 2,500 kilometers (1,550 miles) southwest of Australia. But three days of searching have produced no confirmed signs of the plane.One of the objects spotted in the earlier satellite imagery was described as 24 meters (almost 80 feet) in length and the other was 5 meters (15 feet).
The Boeing 777-200 is about 64 meters (209 feet) long with a wingspan of 61 meters (199 feet) and a fuselage about 6.2 meters (20 feet) in diameter, according to Boeing's website.
In a statement on its website announcing China's find, the State Administration of Science, Technology and Industry for National Defense did not explain why it took four days to release the information. But there was a similar delay in the release of the initial satellite images because experts needed time to examine them.
Two military planes from China arrived Saturday in Perth and were expected on Sunday to join Australian, New Zealand and U.S. aircraft in the search. Japanese planes will arrive Sunday and ships were in the area or on their way.
Erik van Sebille, an oceanographer at the University of New South Wales in Sydney, said the currents in the area typically move at about one meter (yard) per second but can sometimes move faster.
Based on the typical speed, a current could theoretically move a floating object about 173 kilometers (107 miles) in two days.
But even if both satellites detected the same object, it may be unrelated to the plane. One possibility is that it could have fallen off a cargo vessel.
Warren Truss, Australia's acting prime minister while Abbott is abroad, said before the new satellite data was announced that a complete search could take a long time.
"It is a very remote area, but we intend to continue the search until we're absolutely satisfied that further searching would be futile - and that day is not in sight," he said.
"If there's something there to be found, I'm confident that this search effort will locate it," Truss said from the base near Perth that is serving as a staging area for search aircraft.
Aircraft involved in the search include ultra-long-range commercial jets and P3 Orions, the maritime safety authority said.
Because the search area is a four-hour flight from land, the Orions can search for about only two hours before they must fly back. The commercial jets can stay for five hours before heading back to the base.
A small flotilla of ships from China will also join the hunt, along with a refueling vessel that will allow ships to stay in the search area for a long time, Truss said.
Malaysian Defense Minister Hishammuddin Hussein said conditions in the southern corridor were challenging.
The area where the objects were identified by the Australian authorities is marked by strong currents and rough seas, and the ocean depth varies between 1,150 meters (3,770 feet) and 7,000 meters (23,000 feet). In addition, Hishammuddin said a low-level warning had been declared for Tropical Cyclone Gillian, although that was north of Australia and closer to Indonesia.
The missing plane, which had been bound for Beijing, carried 153 Chinese passengers. In the Chinese capital on Saturday, relatives of the passengers rose up in anger at the end of a brief meeting with Malaysia Airlines and Malaysian government officials.
"You can't leave here! We want to know what the reality is!" they shouted in frustration over what they saw as officials' refusal to answer questions. The relatives gave reporters a statement saying they believe they have been "strung along, kept in the dark and lied to by the Malaysian government."
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. They are unsure what happened next.
Police are considering the possibilities of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.
Malaysia asked the U.S. for undersea surveillance equipment to help in the search, said Rear Adm. John Kirby, a Pentagon spokesman. Defense Secretary Chuck Hagel promised to assess the availability of the technology and its usefulness in the search, Kirby said. The Pentagon says it has spent $2.5 million to operate ships and aircraft in the search and has budgeted another $1.5 million for the efforts.___
Griffith reported from Perth, Australia. Associated Press writers Todd Pitman and Eileen Ng in Kuala Lumpur, Malaysia, Kristen Gelineau in Sydney and Didi Tang and Christopher Bodeen in Beijing contributed to this report.