It is "highly unlikely" debris from the missing flight MH370 will ever be found floating on the ocean surface, Australia's prime minister has admitted.
The hunt for the Malaysia Airlines plane, now missing for 52 days, will continue underwater, and could take many more months, Tony Abbott told a Canberra press conference.
The search area will also be widen to take in a larger area of the Indian Ocean.
"I am now required to say to you that it is highly unlikely at this stage that we will find any aircraft debris on the ocean surface," Abbott said.
"By this stage, 52 days into the search, most material would have become waterlogged and sunk."
The Boeing 777 was carrying 239 passengers and crew to Beijing from Kuala Lumpur when it disappeared, on March 8. Satellite images suggest the plane veered off course toward the southern Indian Ocean and may have run out of fuel in the middle of the sea.
"I want the families to know, I want the world to know, that Australia will not shirk its responsibilities in this area," he added. "We will do everything we humanly can to solve this mystery."
"We will not let people down and while the search will be moving to a new phase in coming weeks, it certainly is not ending."
The US Navy's Bluefin-21 underwater device has scoured the search area off Australia's western coast and found nothing, meaning the search area must be expanded.
Asked if it was possible that nothing will ever be found from the missing plane, Abbott said: "Of course it's possible, but that would be a terrible outcome because it would leave families with a baffling uncertainty forever.
"The aircraft plainly cannot disappear - it must be somewhere."
The next stage in the underwater search will mean searching an area roughly 430 miles long and 50 miles wide.
Private companies will now be contracted to the search, Abbott said. “The Australian Government, in consultation with the Malaysian Government is willing to engage one or more commercial companies to undertake this work and this work would be done under contract to the Australian government," he told reporters.
“While the search will be moving to a new phase in coming weeks, it certainly is not ending,” he added.
The projected cost of the search is in the region of £33m.
Earlier this month a Chinese vessel picked up several pings from what was believed to be a black box, which an Australian ship also detected, but Abbott said he remained “baffled” as to why the box had not been found.
“It may turn out to be a false lead but, nevertheless, it’s the best lead we’ve got and we are determined to pursue it.”