After the U.S. Navy robot submarine Bluefin-21 completed its first full scan of the seabed some 2,000 km (1,240 miles) west of the Australian city of Perth, authorities said they had reduced the search area based on further analysis of what they believe may be signals from the plane's black box.
It came as an air-and-sea search was expected to be scaled down almost six weeks after Malaysia Airlines flight MH370 disappeared from radar screens mid-flight with 239 people on board.
A series of "pings" recorded this month have led searchers to the remote stretch of ocean in the belief that the signals may have come from the plane's black box recorders.
However, with no pings received in more than a week and the black box's battery now 10 days past its approximate expiry date, authorities are relying on the Bluefin drone.
On April 15, a U.S. Naval spokesman said the drone would take up to two months to search its designated area, but on Thursday the Australian Joint Agency Coordination Centre said that was now incorrect.
"Since the US Navy provided comment some days ago, the underwater search has been significantly narrowed through detailed acoustic analysis conducted on the four signal detections made by the Towed Pinger Locator," the JACC said in a statement.
The analysis had created a "reduced and more focused underwater search area".
"The current underwater search efforts are being pursued to their completion so we can either confirm or discount the area as the final resting place of MH370," the statement said.
AIRCRAFT CONTINUE TO SEARCH
Meanwhile, a separate lead in the search, a sample taken from an oil slick picked up in the area, had been analysed and was found not to be aircraft engine oil or hydraulic fluid, the JACC said, suggesting it was not related to an aircraft.
On Monday, the search coordinator, retired Air Chief Marshal Angus Houston, said the air and surface search for debris would likely end in three days as the operation shifted its focus to the largely unmapped area of ocean floor.
However, authorities said on Thursday up to 10 military aircraft, two civil aircraft and 11 ships would still search an area totalling about 40,000 square km (15,450 square miles).
That would suggest searchers, under pressure from the families of those on board the plane, still hold some hope of finding floating wreckage.
Australian Prime Minister Tony Abbott was quoted by the Wall Street Journal on Wednesday as saying that "we believe that (underwater) search will be completed within a week or so. If we don't find wreckage, we stop, we regroup, we reconsider".
Asked by Reuters on Thursday to clarify Abbott's comments to the newspaper, his office said he was only suggesting that authorities may change the area being searched by the Bluefin-21 drone, not that the search would be called off.
Malaysia's defence minister, Hishammuddin Hussein, vowed that the search would continue even if there could be a pause to regroup and reconsider the best area to scour.
"The search will always continue. It's just a matter of approach," he told a news conference in Kuala Lumpur.
He said Abbot remained in close contact with Malaysian Prime Minister Najib Razak and the two had spoken on Thursday to discuss the search.
"They've been looking for 40 days and haven't found anything floating yet," Geoffrey Dell, Associate Professor of Accident Investigation and Forensics at Central Queensland University, told Reuters.
"You'd have to start saying there's either nothing to find or let's move elsewhere," he said.