The search for the missing Malaysian plane is entering a “new phase”, Australia has announced, after the initial undersea search found nothing.
PM Tony Abbott said that “a much larger” area of the ocean floor would now be targeted.
But he said it was “highly unlikely” any surface wreckage would be found, and suspended aerial searches.
Malaysia Airlines flight MH370 went missing on 8 March as it flew from Kuala Lumpur to Beijing.
The plane, carrying 239 people, disappeared off radar over the South China Sea.
Officials say that, based on satellite information, they believe it ended its journey in seas north-west of the Australian city of Perth, far from its planned path.
Investigators have given no reason yet as to why the plane flew so far off course. Finding the “black box” flight recorders is seen as key to understanding what happened.
Mr Abbott made his announcement at a news conference in Canberra.
“It is now 52 days since Malaysia Airlines Fight MH370 disappeared and I’m here to inform you that the search will be entering a new phase,” he said.
By now, he said, most debris would have become water logged and sunk, so operations would now focus on “searching the ocean floor over a much larger area”.
So far, a robot submersible called the Bluefin-21 has been scouring the seabed in the location of acoustic signals heard on 8 April believed to have originated from the plane’s flight recorders.