The search zone for missing Malaysia Airlines flight MH370 will be expanded if the plane isn't found in the part of the Indian Ocean currently being scoured.

About 60 per cent of the current 60 thousand square kilometre search zone off the West Australian coast has been combed.

Deputy Prime Minister Warren Truss says if the Boeing 777 isn't found by the time that's been completed - which is expected next month - the search area will be doubled to 120 thousand square kilometres.