Australian Transport Safety Bureau chief Martin Dolan said the underwater search off the West Australian coast for the missing Malaysia Airlines MH370 will be called off as soon as July, unless significant new evidence emerges.

Dolan who is the person in charge of the search for the missing plane, said the Australian government had commissioned a search covering 120,000 square kilometres and they had about 15,000 square kilometres left to go, ABC.net.au reported.

"At this stage I remain optimistic that we will find the aircraft in a defined search area," he told the portal.

"We are at the point of the search where we have to contemplate the possibility that we won't find it," he was quoted saying.

The Boeing 777 went missing in March 2014 on a routine flight from Kuala Lumpur to Beijing with 239 passengers and crew onboard.

Adding that it was a matter of probability, and not certainty, that the aircraft would be found in the area they were searching, Dolon acknowledged that the news would upset and disappoint families of those onboard MH370.

He told the portal that "they could only do what the Government gave them the resources to do."

Several debris had washed up in Africa with the latest being in South Africa and the Mauritian island of Rodrigues but Dolon said there was not much information to be found in the bits of wreckage found.

"It's very hard to determine from them much about what's happened to the aircraft at the end of its flight," he said.

He said once they have completed the search in the defined area without locating the aircraft, then they will know that the aircraft was not in that area.

Department of Civil Aviation director-general, Datuk Seri Azharuddin Abdul Rahman said there was a 90 percent possibility that the two debris found in South Africa and the Mauritian island of Rodrigues came from the missing MH370.

READ: 'Almost certainly' means it's 90 percent MH370, says DCA

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He said the percentage could be construed as 'almost certainly', as mentioned by the Malaysian International Civil Aviation Organisation (ICAO) Annex 13 Safety Investigation Team when it concluded that the debris were consistent with the panel of the Boeing 777 aircraft.

That conclusion came after a team of international experts completed its investigation in Australia on a 'cowling' part of an engine, with half of the Rolls-Royce logo and fragments of cabin interior panels visible.

So far, there have been five debris found linked to MH370.

The first was a wing section 'flaperon' found on La Reunion in France in July 2015, which has since been confirmed as MH370's; then a horizontal stabiliser from a tail section found in Mozambique in December 2015; the third a stabiliser panel with a "No Step" stencil found in Mozambique last February; the fourth an engine cowling bearing a Rolls-Royce logo found last March in Mossel Bay; and then a fragment of interior door panel found in Rodrigues Island, also found in March.