Australia will contribute an extra Aus$79.6 million (US$63.4 million) over the next two years to the search for missing airline MH370 if it is not found in the current probe, budget documents showed Tuesday.

The hunt for the plane, spanning 60,000 square kilometres (23,166 square miles), is focusing on a narrow strip of water in the remote southern Indian Ocean and is due to end later this month.

No sign of wreckage of the Malaysian Airlines jet, which was carrying 239 people when it disappeared on March 8 last year en route from Kuala Lumpur to Beijing, has been found despite an intensive air and sea hunt.

"The government will provide Aus$79.6 million over two years from 2014-15 to continue the search for Malaysian Airlines flight MH370 should the aircraft not be located in the current search area," the budget papers said.

"This will increase the search area by an additional 60,000 square kilometres to 120,000 square kilometres."

The extended hunt was first flagged by the Australian, Malaysian and Chinese governments last month. Most of the passengers were Chinese.

Some Aus$14.4 million has already been allocated this financial year to the agency leading the search, the Australian Transport Safety Bureau.

The government said the cost could be lowered by contributions from other countries.

"The cost of this measure will be offset by financial contributions to the search from other countries," the budget outlined. "The actual cost will depend on a number of factors, including the length of the search."

Four specialist vessels are scouring the depths of the search zone off the west coast of Australia after the ocean floor was closely mapped last year.

The ships, including three from Dutch company Fugro, are carrying specialist equipment including towed sonar that can scan some 10 kilometres below the surface.