An underwater drone will now be used in the hunt for the missing Malaysian plane, but searchers warn it could take months or even years before anything is found.
The Malaysian Airlines plane vanished en route from Kuala Lumpur to Beijing with 239 people on board on 8 March, with still no clue as to the cause of the disappearance.
Several sonic 'pings' which authorities have said are consistent with a plane's black box recorder have been detected by ships in the search area. However, the last pings were detected on 8 April and the batteries on Flight MH370's black boxes are now past their 30-day lifespan.
In a media briefing on Monday, retired Air Chief Marshal Angus Houston said there had been no acoustic trace of the black box detector for six days. He said the Australian Defence Force would deploy the autonomous underwater vehicle Bluefin-21 as soon as possible, the ABC reports.
The drone will map the sea floor using sonar. However, it can only cover 40 square kilometres a day and it could be months or even years before anything is found. Air Chief Marshall Houston said the equipment is also working at the very edge of its depth limit.
An oil slick has also been spotted in the vicinity of the search area, but it is unclear whether it is from the Boeing 777, he said.
"An area new to man", is how the Australians have described the far reaches of the Indian Ocean where the robotic submarine will search for any trace of Flight MH370. It will be deployed in the same vicinity as four underwater signals that were consistent with an aircraft's black box, the BBC reports.
Each mission using the Bluefin-21 is expected to take 24 hours. It will be painstaking, slow work and doesn't bring any guarantees that wreckage will be found. However, Australian seachers believe the acoustic pulses heard a week ago remain their best lead to locating the plane so far.
Malaysia says no mid-flight call
Malaysia has rejected claims that phone calls were made from Flight MH370 before it vanished, but refused to rule out any possibility in a so far fruitless investigation over the cause of the jet's disappearance.
The New Straits Times, quoting an anonymous source, had reported on Saturday that co-pilot Fariq Abdul Hamid made a call which ended abruptly, possibly "because the aircraft was fast moving away from the (telecommunications) tower".
There had also been unconfirmed reports of calls by the Malaysia Airlines plane's captain Zaharie Ahmad Shah before or during the flight.
However, Malaysian Transport Minister Hishammuddin Hussein told reporters on Sunday that authorities had no knowledge of any calls made from the jet's cockpit.
Mr Hishammuddin also said no passenger on the plane had been cleared in the criminal investigation into the fate of the flight, clarifying an earlier indication from Malaysia's police chief.
The pilots have come under intense scrutiny since the plane disappeared.