Updated

The underwater hunt for the missing Malaysia Airlines jet will be expanded to include a massive swath of ocean floor that may take up to eight months to thoroughly search, Australia's prime minister said Monday.

The U.S. Navy's Bluefin 21 robotic submarine has spent weeks scouring the initial search area for Flight 370 in the remote Indian Ocean far off Australia's coast, but has found no trace of the missing plane, Prime Minister Tony Abbott said. Officials are now looking to bring in new equipment that can search a larger patch of seabed for the plane, Abbott said.

"It is highly unlikely at this stage that we will find any aircraft debris on the ocean surface. By this stage, 52 days into the search, most material would have become waterlogged and sunk," Abbott told reporters. "Therefore, we are moving from the current phase to a phase which is focused on searching the ocean floor over a much larger area."

Radar and satellite data show the jet carrying 239 passengers and crew veered far off course on March 8 for unknown reasons during a flight from Kuala Lumpur, Malaysia, to Beijing. Analysis indicates it would have run out of fuel in the remote section of ocean where the search has been focused. But not a single piece of debris has been recovered since the massive multinational hunt began.

The Bluefin has been creating a three-dimensional sonar map of the ocean floor for more than two weeks near where signals consistent with airplane black boxes were heard on April 8. The original underwater search zone was about 400 square kilometers (150 square miles).

Crews will now begin searching the plane's entire probable impact zone, an area 700 kilometers (430 miles) long and 80 kilometers (50 miles) wide, Abbott said.

That will be a monumental task — and one that will take time, warned Angus Houston, head of the search effort.

"If everything goes perfectly, I would say we'll be doing well if we do it in eight months," Houston said, adding that weather and technical issues could cause the search to drag on well beyond that estimate.

Australian officials will be contacting private companies to bring in additional sonar mapping equipment that can be towed behind boats to search the expanded area at an estimated cost of $60 million, Abbott said. It could take officials several weeks to organize contracts for the new equipment and in the meantime, the Bluefin will continue to scour the seabed, Abbott said.

So far, each country involved in the search has been bearing its own costs. But Abbott said Australia would now seek contributions from other countries to help pay for the cost of renting the new equipment.

Despite the Bluefin's failure to find any wreckage, the prime minister said he has a "considerable degree of confidence" that the underwater signals picked up by sound-detecting equipment on April 8 were from the plane's black boxes.

"We're still baffled and disappointed that we haven't been able to find undersea wreckage based on those detections, and this is one of the reasons why we are continuing to deploy the Bluefin 21 submersible — because this is the best information that we've got," Abbott said. "It may turn out to be a false lead, but nevertheless it's the best lead we've got."

"I want the families to know, I want the world to know, that Australia will not shirk its responsibilities in this area. We will do everything we humanly can ... to solve this mystery," Abbott added. "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."

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Associated Press writer Kristen Gelineau in Sydney contributed to this report.