CANBERRA, March 20, 2014  - The largest object sighted in the search for missing Malaysia Airlines flight MH370 is 24 metres (79 feet), with a second, smaller object also spotted, Australian authorities said Thursday.

Australian Maritime Safety Authority (AMSA) official John Young said the largest object sighted "was assessed as being 24 metres. There is another one that is smaller than that."

"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," Young said.

"But we need to get there, find them, see them, assess them, to know whether it's really meaningful or not."

A merchant ship was expected to arrive in the vicinity around 0700 GMT and the Australian naval vessel HMAS Success, which is capable of retrieving any debris, is some days away.

AMSA had earlier said it had "significantly refined" the vast area of the Indian Ocean that Australia was searching, following an analysis of the jet's fuel reserves.

Sketchy radar and satellite data had initially resulted in investigators proposing two vast search corridors, stretching south into the Indian Ocean and north over South and Central Asia.

Most analysts had favoured the southern corridor, pointing out the unlikelihood of the airliner passing undetected over the nearly one dozen countries in the northern arc.

The international search has been marked by numerous false leads, and Abbott sought to temper expectations.

"We must keep in mind the task of locating these objects will be extremely difficult and it may turn out that they are not related to the search for flight MH370," he said.

To be updated...