As planes spent a third day hunting for two large objects spotted by satellite in the southern Indian Ocean, Australian officials today said they were far from giving up on what remains the strongest lead in the search for Malaysia Airlines Flight 370.

Two military planes from China arrived in Perth to help search a remote stretch of ocean about 1,550 miles to the southwest. Australian, New Zealand and US planes were already involved, two Japanese planes will arrive on Sunday, and ships were in the area or on their way.

Australian prime minister Tony Abbott, on an official visit to Papua New Guinea, said weather hampered the search earlier but conditions were improving.

“There are aircraft and vessels from other nations that are joining this particular search because tenuous though it inevitably is, this is nevertheless the first credible evidence of anything that has happened to Flight MH370,” Abbott said.

A satellite spotted two large objects in the area earlier this week, raising hopes of finding the Boeing 777, which disappeared on March 8 with 239 people on board less than an hour after taking off from Kuala Lumpur.

One of the objects was almost 80 feet in length and the other was 15 feet. The objects could be unrelated to the plane; one possibility is that they fell off one of the cargo vessels that travel in the area.

Warren Truss, Australia’s acting prime minister while Abbott is travelling abroad, said 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 two ultra-long-range commercial jets and four P3 Orions, the Australian Maritime Safety Authority said.

Because the search area is a four-hour flight from land, the Orions can search for only about two hours before they must fly back. The commercial jets can stay for five hours before heading back to the base.

Two merchant ships were in the area, and the HMAS Success, a navy supply ship, was due to arrive late this afternoon.

Australian maritime officials also were checking for updated satellite imagery. The satellite images that show the objects were taken March 16, but the search in the area did not start until Thursday because it took time to analyse them.

The Chinese planes that arrived in Perth today were expected to begin searching on Sunday. 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.

The missing plane, which had been bound for Beijing, carried 154 Chinese. In the Chinese capital today, 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”.

In Kuala Lumpur, Malaysian defence minister Hishammuddin Hussein called the process “a long haul” as he thanked the more than two dozen countries involved in a search that stretches from Kazakhstan in Central Asia to the southern Indian Ocean.

Malaysia asked the US for undersea surveillance equipment to help in the search, said John Kirby, a Pentagon spokesman. Defence secretary Chuck Hagel promised to assess the availability of the technology and its usefulness in the search, Kirby said.

Some questions had been raised about the cargo of the missing plane because it contained lithium ion batteries. Malaysia Airlines issued a statement saying it was in compliance with the International Civil Aviation Organisation and the International Air Transport Association requirements and classified as “non-dangerous goods”.

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.