Eight aircraft were set to join the search Sunday for missing Malaysia Airlines 3786. Flight 370 in the southern Indian Ocean, as Australian Prime Minister Tony Abbott said authorities had a number of credible leads, including satellite images of an object in the area from Beijing.

A Chinese defense agency said Saturday an analysis of satellite images showed a large object, 22 meters (72 feet) long and 13 meters wide, floating in the southern Indian Ocean. Mr. Abbott said the Chinese images were consistent with earlier satellite photos of two bits of debris, the largest of which was around 79 feet long, revealed Thursday.

“It is still too early to be definite, but obviously we have now had a number of very credible leads and there is increasing hope—no more than hope—that we might be on the road to discovering what happened to this ill-fated aircraft,” Mr. Abbott told reporters as he prepared to board a flight back to Australia from an official visit to neighboring Papua New Guinea.

Among several developments in the past 24 hours described by Mr. Abbott as “significant” was the discovery of a number of small items, including a wooden pallet and strapping material, by searchers.