MH370
French gendarmes and police inspecting a large piece of plane debris which was found on the beach in Saint-Andre, on the French Indian Ocean island of La Reunion, 29 July, 2015Prisca Bigot/ Reuters

The missing Malaysia Airlines flight MH370 plane 'is very likely' to be found before July, according to the man leading the $133.3 billion search.

Martin Dolan, the head of the Australian Transport Safety Bureau, said that as 75% of the 120,000 sq km search area had been combed, it was likely the operation would recover the plane in the remaining unsearched 25% of the area – which will be covered by the operation's end date of July 2016.

"It's as likely on the last day [of the search] as on the first that the aircraft would be there," Dolan told The Guardian. "We've covered nearly three-quarters of the search area, and since we haven't found the aircraft in those areas, that increases the likelihood that it's in the areas we haven't looked at yet.

Flight MH370 went missing en route from Kuala Lumpur to Beijing in March 2014 with 239 people on board, with no trace whatsoever of the flight until last July, when a piece of debris from the plane was found on Reunion.

A further piece of debris was found on 3 March by MH 370 hunter Johnny Begue, who found the first piece in July 2015, although it has not been verified as coming from MH370 as yet and has been handed over to authorities to determine whether or not it is another piece of the Boeing 777.

Meanwhile another piece of potential debris was found in Mozambique by Blaine Alan Gibson, 58, who has funded his own year-long search for the missing plane.

"We've still got some serious area to cover, including some areas in the assessment that are highly prospective for finding the aircraft, and the aircraft's very likely there," Dolan said.

"We'll cover those very thoroughly and I hope our next conversation is going to be about how we found the aircraft."

Following the plane's disappearance, a number of conspiracy theories were put forward including that the plane was hijacked or that the pilot was not at the controls at the time of the crash, while earlier in March a UFO spotter said he believed he could have located the plane in the Cape of Good Hope off the coast of South Africa.

If the plane has not been located by July, the search will come to an end and investigators will need to look at one of the other theories put forward, including whether the pilot intended for the plane to go down.