Australia's prime minister said Sunday he was hopeful clues will emerge soon to help find Flight 370 even though searchers again failed to find jet debris, as relatives of Chinese passengers on the plane protested in Malaysia to demand the government apologize over its handling of the search.
An increasing number of ships are scouring an area of the Indian Ocean off western Australia after a new search zone was identified Friday, but the only objects scooped up by the vessels so far have been "fishing equipment and other flotsam" not connected to the Malaysia Airlines plane that crashed March 8 with 239 people on board, the Australian Maritime Safety Authority said in a statement.
Australian Navy Commodore Peter Leavy told reporters that "there has been no discrete debris associated with the flight."
In Sydney, Australian Prime Minister Tony Abbott insisted that the "intensifying search effort" was positive because objects "have been recovered from the ocean" in the zone after a weeklong search in another area spotted items from planes that ships never managed to find.
The maritime safety authority said nine planes took part in the search Sunday, leaving in staggered times from a military base near the western city of Perth. Eight ships were on the scene, including the Australian navy supply ship HMAS Success, which was designated as the vessel that will store any wreckage found.
Leavy said the operation in the new search zone is complicated because it lies in a shipping lane where sea trash is common.
Searchers were hampered by rain and low clouds, but were still able to look for signs of plane debris with visibility of about 10 kilometres (6 miles). It takes planes about 2 1/2 hours to get to the area, giving them five hours of searching time before they must return to base.
Objects spotted so far include three with white, red and orange colours by a Chinese Ilyushin IL-76 plane, China's official Xinhua News Agency said. The missing Boeing 777's exterior was red, white, blue and grey.
In Malaysia, several dozen Chinese relatives of passengers of Flight 370 demanded that the Malaysian government apologize for its handling of the search for the plane and for the prime minister's announcement that it crashed into the southern Indian Ocean before any wreckage was found.
The group staged its protest at a hotel near Kuala Lumpur, Malaysia's largest city, hours after flying in from Beijing, waving banners that read "We want evidence, truth, dignity" and "Hand us the murderer. Tell us the truth. Give us our relatives back." They also demanded a meeting with Prime Minister Najib Razak.
Two-thirds of the 227 passengers aboard the plane, which disappeared en route to Beijing from Kuala Lumpur, were Chinese. China has urged Malaysia to be more open about the investigation, while Malaysian officials have defended their handling of the probe and the information they have provided to passengers' relatives.
Searchers for a full week relied on satellite data from various countries as they tried to find the plane in a different zone to the south of the current area, but abruptly shifted course Friday after authorities concluded the plane could not have travelled as far as they had thought based on its estimated speed and fuel consumption.
That prompted the change in the hunt for the plane's likely entry point into the sea and its "black boxes," which should contain clues to what caused the aircraft to be so far off-course.
An Australian warship with an American black box detector and specialists aboard to use it was set to depart Sunday from a port near Perth to join the search. It will still take three to four days for the ship, the Ocean Shield, to reach the search zone — an area roughly the size of Poland, about 1,850 kilometres (1,150 miles) west of Australia.
"The ship will take part in the surface search until the debris is positively identified and an underwater search area is then predicted," U.S. Navy Captain Mark Matthews told reporters.
In addition to the U.S. Navy's Towed Pinger Locator used to hear pings from the black boxes, the ship will also have an unmanned underwater vehicle and other acoustic detection equipment that will be used to try to find the wreckage on the seabed under the search zone.
But the search area is so huge that investigators are first hoping to find floating wreckage of the plane so they could set a smaller zone using sophisticated analysis to determine a location from where the debris drifted. Even if they do that, recovery of the jet's flight data and cockpit voice recorders could be complicated.
Despite the huge area defined for searching, one advantage is that the seabed in this part of the Indian Ocean is generally flat with the exception of a steep slope and a deep drench near its southern end.
The area is dominated by a muddy ocean floor known as Broken Ridge, which is actually a plateau where depths range from as shallow as about 800 metres (2,625 feet) to about 3,000 metres (9,843 feet).
At the edge of the plateau closest to Antarctica is the Diamantina trench, which seafloor mappers have found is as deep as 5,800 metres (19,000 feet) within the confines of the search zone, though it could be deeper in places that have not been measured.
Matthews said the Navy's ping locator has the "capability to do search and recovery operations down to a depth of 20,000 feet."
Data on the black boxes may help investigators solve what has become one of aviation's big mysteries — what happened to Flight 370, with speculation ranging from equipment failure and a botched hijacking to terrorism or an act by one of the pilots.
Australian Prime Minister Abbott also announced that a former Australian defence chief, Air Chief Marshal Angus Houston, will lead a new search and recovery operations centre in Perth to co-ordinate the international effort.