The Australian Maritime Safety Authority (AMSA) on Thursday revealed the imagery had been captured by its rescue coordination centre.

It indicates debris near the search zone in the Southern Indian Ocean, some 2300 kilometres southwest of Perth.

‘‘They may not be related to the aircraft,’’ an AMSA statement said.

A RAAF aircraft arrived at the area just before 2pm and three more military aircraft, including two from the United States and New Zealand, are expected to reach the area later on Thursday.

An Australian Hercules will drop marker buoys in the area highlighted by the satellite imagery

The marker buoys provided information about water movement to assist drift modelling.

‘‘They will provide an ongoing reference point if the task of relocating the objects becomes protracted,’’ AMSA said.

Weather conditions in the area are moderate but visibility is poor.

 A merchant ship that responded to a shipping broadcast issued by Rescue Coordination Australia on Monday is expected to arrive in the area about 6pm.

John Young, emergency response division general manager at AMSA, said the focus was to continue the search with all available ships and aircraft.

‘‘The objects are relatively indistinct on the imagery,’’ he said.

‘‘The are objects of a reasonable size and probably awash with water.’’

The largest was assessed as being about 24 metres.

 Mr Young said the ocean in the area was thousands of metres deep.

 ‘‘AMSA is doing its level best to find anyone that might have survived,’’ he said when asked what advice he had for families of the 239 people who were on the missing flight.

 MH370 disappeared just hours after leaving Kuala Lumpur for Beijing early on Saturday March 8.

AAP