(Adds quotes and details of search area)
By Matt Siegel
SYDNEY, April 28 (Reuters) - The chance of finding floating debris from a missing Malaysia Airlines jetliner has become highly unlikely, and a new phase of the search would focus on a far larger area of the Indian Ocean floor, Australian Prime Minister Tony Abbott said on Monday.
The international search effort for Malaysia Airlines Flight MH370, which vanished on March 8 with 239 people on board, has so far failed to turn up any trace of wreckage from the plane.
Given the amount of time that has elapsed, Abbott said that efforts would now shift away from the visual searches conducted by planes and ships and towards underwater equipment capable of scouring the ocean floor with sophisticated sensors.
Abbott admitted, however, that it was possible nothing would ever be found of the jetliner.
"We will do everything we humanly can, everything we reasonably can, to solve this mystery," he told reporters in Canberra.
Authorities had focussed their search on a 10 square km (6.2 square mile) stretch of seabed about 2,000 miles northwest of Perth after detecting what they suspected was a signal from the plane's black box recorder on April 4.
But Abbott's comments appeared to be an acknowledgement that the search by a U.S. Navy Bluefin-21 underwater drone in that refined area had failed find any sign of the jetliner.
Abbott said that the new search area, which spans 700 km by 80 km, could take between 6-8 months to completely examine.
(Reporting by Matt Siegel; Editing by Simon Cameron-Moore)