Australian officials said Sunday that a wooden cargo pallet along with belts or straps have been spotted in the remote Indian Ocean by one of the aircraft deployed in the hunt for a missing Malaysian jet.

The objects were seen by a civilian aircraft assisting in the search for Malaysia Airlines MH370 on Saturday in what the Australian Maritime Safety Authority confirmed was the "first visual sighting in the search so far".

"Part of the description was a wooden pallet and a number of other items which were nondescript around it and some belts of some different colours around it as well, strapping belts of different lengths," AMSA aircraft operations coordinator Mike Barton said.

"We tried to refind that yesterday, one of the New Zealand aircraft, and unfortunately they didn't find it. That's the nature of it -- you only have to be off by a few hundred metres in a fast-travelling aircraft," he told a press briefing.

Barton said Sunday's search, which will involve four military and four civilian aircraft, would return to the area to try and zero in on the objects again.

Aviation experts had advised that wooden pallets were quite commonly used to pack goods in planes, Barton added, describing it as a "possible lead".

Such pallets were usually packed into another container loaded into the belly of the aircraft he said, adding however that they were also used in the shipping industry.

He cautioned that the nearby straps "could be anything" and "until we refind these items and have a good look at them it's hard to say whether they are associated with this or not."

A "methodical search" would also continue of a 59,000 square kilometre (22,800 square mile) expanse of sea to try and locate large items captured by satellite imagery on March 16 and 18.

Barton said the operation had shifted away from an earlier emphasis on radar to focus on visual examination "of a more defined area based on the satellite imagery."

He said looking into the sun and through haze from a much lower altitude than a satellite was making things difficult for search crews.

Sunday's weather was not as good as the previous day's, with sea fog and low cloud hampering visibility early in the day, though Barton said it appeared to be clearing and he was hopeful of a "full search in with some good conditions."

But the major challenge was the site's remoteness.

"The aircraft are operating at extreme ranges... At 2,500 kilometres away they're operating at the limits of their endurance and only having a short period of one to two hours in the search area and back again," he said.