The swathe of Indian Ocean where acoustic "pings" were detected has been ruled out as the crash zone of missing Malaysia Airlines passenger jet after a lengthy underwater search.

The Joint Agency Coordination Centre said on Thursday it had completed the search of an area off the Australian coast where pings were detected in early April, with no success. 

An unmanned submarine had searched 850sqr km but had found no sign of the plane.

"The Australian Transport Safety Bureau has advised that the search in the vicinity of the acoustic detections can now be considered complete and in its professional judgement, the area can now be discounted as the final resting place of MH370," the agency said in a statement.

The statement came after a US official said he believed the "pings" did not come from the black box of the missing jet.

Michael Dean, the US navy's civilian deputy director of ocean engineering, said on Wednesday that most countries agreed that the sounds came from a man-made source unrelated to the jet.

The Malaysia Airlines jet vanished on March 8 with 239 people on board.

The centre said the operation would now move to the next phase involving scanning the unmapped ocean bed with all existing information and analysis reviewed to define a search zone of up to 60,000sqr km.

A Chinese survey ship, Zhu Kezhen, is mapping areas of the sea floor in preparation for the commercially contracted deep ocean search, which is expected to begin in August and take up to 12 months, JACC said.

Source: Agencies