A new phase in the search for Malaysia Airlines Flight MH370 will involve deep-water searches of the sea floor that may take as much as a year to finish, officials say.

The government of Australia says it has selected a firm in the Nethelands, Fugro NV, to search southern Indian Ocean waters and seafloor for wreckage of the flight that went missing in March with 239 people on board.

There were several bidders on the Australian contract, including oil-and-gas exploration firms and specialist salvage recovery companies.

Fugro was chosen for its ability to conduct lengthy operations with multiple ships and rotating crews, a necessity for the planned 300-day operation, officials said.

The company had decades of experience helping its clients search underwater topography for oil and gas, gaining experience in sea-floor mapping and exploration.

"I remain cautiously optimistic that we will locate the missing aircraft within the priority search area," Australian Deputy Prime Minister Warren Truss said. "This search will obviously be a challenging one."

In the international search effort, the Woods Hole Oceanographic Institution in Massachusetts will provide two autonomous underwater research vehicles if a possible debris field is located, Donald Hussong, a highly-regarded deep-sea sonar expert, said.

The Remus 6000 submersibles are the same ones that were used to locate the wreckage of Air France Flight 447 in the Atlantic Ocean in 2011, two years after it went down in bad weather.

The hunt for the Malaysian Boeing 777 will be a difficult one, as little is known of the ocean floor in the region where the airliner is presumed to have gone down.

"It's one of the least mapped areas in the world," Hussong said.

Fugro will begin its search in September, surveying the ocean floor off the coast of southwest Australia using two ships with sonar scanning capabilities to scour more than 23,000 square miles of ocean.

The search area has been defined using satellite data that tracked the last hours of the airliner's flight, although the data can only suggest approximate possible paths.

In addition to the Dutch vessels working under contract to the Australian government, Malaysia will contribute four ships to the search and a Chinese research vessel will continue its sea-floor searches until mid-September, officials said.

The hunt for the Flight 370, which disappeared on a scheduled flight from Kuala Lumpur to Beijing, is already the longest in the history of aviation.