A US Navy official has claimed underwater signals detected in the search for the missing Malaysia Airlines plane came from a search boat or the ping detector itself.

Families of passengers on board the missing flight say they have been left feeling "helpless" after a US Navy spokesperson said there is international agreement the sounds came from a source unrelated to flight MH370.

Steve Wang, whose mother (57) was on board the fated flight said "We all feel quite helpless; we don't know who to turn to now".

"When (Australian Prime Minister) Tony Abbott told the world about the conclusion of the location of the search operation, he was really certain. Now it's not the case at all".

"What evidence brought him to this conclusion is the question we've been asking all along. What has Boeing done to support this initial conclusion in associate with the detection of the pulse signal? Was it Boeing's conclusion or Australia's?".

Mr. Wang, who still has his mother's final voice message she left him just before she boarded the plane, said that more flight data should be released so it can be independently analysed.

"We ask them to release all the evidence so it can be analysed by more people, not just by Inmarsat or the expert team from Malaysia".

Michael Dean, the US Navy's deputy director of ocean engineering said that if the pings came from the plane's black box or voice recorders they would have been found by now.

"Our best theory at this point is that (the pings were) likely some sound produced by the ship...or within the electronics of the towed pinger locator" he told CNN.

"Always your fear any time you put electronic equipment in the water is that if any water gets in and grounds or shorts something out, that you could start producing sound".

The pinger locator was towed by the Australian ship Ocean Shield to listen for underwater signals in the southern Indian Ocean in an area where satellite data indicated the plane went down.

A series of signals it picked up prompted Australian Prime Minister Tony Abbott to say he was "very confident" they were from the black box of the plane that vanished en route to Beijing from Kuala Lumpur with 239 people on board.

But Australia's Transport Safety Bureau (ATSB) has confirmed that Ocean Shield has now left an area of 340 square miles that was being scoured for the passenger jet that disappeared without trace on March 8th.

A statement released by Australia's Joint Agency Coordination Centre said "The ATSB 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 news will add to the agony of the families of the 239 people who were on the flight and who have campaigned tirelessly for authorities not to give up the search.

Some 47 pages of raw satellite data tracking the last known movements of MH370 were released a few days ago following calls from the families for the information to be made public so it could be verified by independent experts.

Despite today's statement, a US Navy spokesman said Mr. Dean's comments were "speculative and premature".