CANBERRA (AFP) - The largest object sighted in the search for missing Malaysia Airlines flight MH370 is 24m, with a second, smaller object also spotted, the Australian authorities said on Thursday.

"The objects are relatively indistinct. The indication to me is of objects that are of a reasonable size and probably awash with water and bobbing up and down over the surface," said Australian Maritime Safety Authority official John Young.

"The largest... was assessed as being 24 metres. There is another one that is smaller than that."