The man in charge of the search for missing Malaysia Airlines flight 370 has confirmed the underwater hunt off the West Australian coast will be called off as soon as July, unless significant new evidence emerges.

Key points: Search of 120,000 kilometre arc has so far failed to find any trace

Search of 120,000 kilometre arc has so far failed to find any trace Small fragments of wreckage have washed up in Africa

Small fragments of wreckage have washed up in Africa Government unlikely to commit more funding for search

The search spanning an arc 120,000 kilometres in length has so far failed to find any trace of the Boeing 777 that went missing in March 2014 on a routine flight from Kuala Lumpur to Beijing with 239 passengers and crew onboard.

Small fragments of wreckage have washed up in Africa, but that has not been enough to convince the Federal Government to commit beyond the $60 million it has already spent.

The chief of the Transport Safety Bureau, Martin Dolan, said the Government had commissioned a search covering 120,000 square kilometres and they had about 15,000 square kilometres left to go.

A piece of debris suspected to be from MH370. ( AFP: Australian Transport Safety Bureau/Blaine Gibson )

"At this stage I remain optimistic that we will find the aircraft in a defined search area," Mr Dolon said.

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

Mr Dolon said that they could only do what the Government gave them the resources to do.

He said he understood the families would be upset and disappointed, "that the closure that would have been associated with finding the aircraft may not occur".

Mr Dolon said it was a matter of probability, and not certainty, that the aircraft would be found in the area they were searching.

"We consider that based on the best advice and analyses from the experts that this was a very high priority search area," he said.

Mr Dolon said tthere was not much information to be found in the five bits of wreckage already 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 added that if they manage to complete the search in the defined area without locating the aircraft, then they will know that the aircraft was not in that area.

'They are clearly hiding something'

Sarah Bajc, an American whose partner was on that plane, said she thought the Malaysian Government were "hiding something".

While the hunt for the hull has continued, the Malaysia investigation has been looking at maintenance history, cargo, Telco traffic from the plane, and the still unexplained first loss of power to MH370.

The plane went dark, then regained power as it hurtled into the night sky, offcourse and unnoticed by the air defence network operatives of Malaysia and Thailand.

The criminal case is still open in Malaysia, and the French still suspect it was a terrorist act.

Ms Bajc said she does not agree with the Malaysian Government's narrative that the puzzle would be solved with the discovery of the wreck.

"That airplane flew for a very long time over Malaysia airspace... And they're saying that their military just didn't see it, right, or they didn't think it was a threat, they thought it was friendly," she said.

"I don't believe that. The Malaysia military is quite sophisticated, they've got one of the best radar coverage systems in this part of the world."