Chinese satellites have spotted a large object floating in the search area for the missing Malaysia Airlines plane that could be debris and has sent ships to investigate, Malaysia said on Saturday.

"Chinese ships have been dispatched to the area. Beijing is expected to make an announcement in a few hours," Malaysian Defence Minister and acting Transport Minister Hishammuddin Hussein told reporters.

Malaysia Plane

This image of an object, which is the focus of Saturday's search efforts in the south Indian Ocean, was captured around noon, on March 18 by a Chinese satellite. (China State Administration of Science, Technology and Industry for National Defense/AP)

He said the object is 22 metres by 13 metres in size. It was spotted about 120 kilometres from two other objects announced by Australia earlier in the search for Malaysia Airlines Flight MH370.

Planes are scouring the southern Indian Ocean for a third day to find possible parts of the plane, which has been missing since it left Kuala Lumpur for Beijing on 8 March, carrying 239 people.

An international team — which includes planes from Australia, New Zealand and the U.S. — has so far failed to find any aircraft debris after an Australian-led search that began Thursday, inspired by satellite images taken March 16.

Two Japanese planes were to join the search on Sunday in an area 2,500 kilometres southwest of Perth, Australia.

The search is continuing amid huge challenges in an area covering 36,000 square kilometres.

'There are strong currents, and also rough seas," Hussein said.