The international search for missing Malaysia Airlines flight MH370 has been expanded to cover a total of 59,000 square km in the southern Indian Ocean, Australia's maritime rescue agency announced Sunday.

The fourth day of the search would cover two areas determined by drift modeling within the same proximity about 2,500 km southwest of the city of Perth, said a statement from the Australian Maritime Safety Authority (AMSA).

The search areas were based on information provided by China with satellite photos taken on March 18 showing an object measuring 22 meters by 13 meters floating in the water.

Although the object's position fell within Saturday's search area, it was not found.

However, AMSA had used the information in the development of the search area taking drift modelling into account.

"The Australian Maritime Safety Authority reiterates this is a challenging search operation and continues to hold grave fears for the passengers and crew on board the missing flight," said the statement.

A total of eight aircraft were involved in Sunday's search operation, including four civil aircraft and a United States Navy P8 Poseidon.

Further attempts would be made to find several "small objects of interest" seen by observers on a civil aircraft on Saturday.

A Royal New Zealand Air Force P3 Orion aircraft with specialist electro-optic observation equipment was diverted to the location, but only reported sighting clumps of seaweed.

It dropped a datum marker buoy to track the movement of the material.

Earlier Sunday, Prime Minister Tony Abbott said in an interview in Papua New Guinea published by his office that two Chinese and two Japanese air force aircraft were joining the search.

He said the chances of recovering some of the spotted objects rose with more aircraft and ships taking part in the search.

"It's 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, no more than hope, that we might be on the road to discovering what did happen to this ill-fated aircraft," he said.

"I want to say that this is a really big international effort and it does show that many countries are capable of pulling together in a time of trouble," said Abbott.

"It is a very important humanitarian exercise. We owe it to the almost 240 people on board the plane; we owe it to their grieving families; we owe it to the governments of the countries concerned to do everything we can to discover as much as we can about the fate of MH370."