An oil slick has been detected in the search area for missing Malaysia Airlines flight MH370.
Officials would deploy an underwater drone to conduct sonar searches for the missing plane, Joint Agency Co-ordination Centre chief Angus Houston said today.
Australian Defence Vessel Ocean Shield, which has previously detected potential black box pings, on Sunday collected an oil sample from the search zone that was being investigated for links to MH370.
Authorities planned to drop an autonomous underwater vehicle to the seafloor of the Indian Ocean and begin a visual search for flight MH370 wreckage, within hours.
Analysis of the four potential black box detections by ADV Ocean Shield in recent weeks has reduced the underwater search zone, Houston said at a press conference in Perth.
"The experts have therefore determined the ADV ocean shield will cease searching with the towed pinger locater later today and deploy the autonomous under water vehicle Bluefin-21," he said.
Travelling at a walking pace, each search mission would take the Bluefin-21 at least 24 hours. It would cover an area of 40 square kilometres on its first day in operation.
It takes the vehicle two hours to reach the sea floor, it would then search for 16 hours, take another two hours to return to the surface and then four hours to download the data it has detected, Houston said.
"The Bluefin-21 in side scan sonar mode transits an active pulse which projects a high resolution 3 dimensional map of the sea floor," he said.
Houston described the seafloor search as a "further step towards visual confirmation" with possibility of detecting aircraft wreckage on ocean floor.
But it would be days before the origins of the oil can be investigated by experts on shore.
As many as 11 military aircraft, one civilian jet and 15 ships were searching an area about 47,644 square kilometres for the missing flight on Monday.
There have been no acoustic detections picked up in the underwater search area since Tuesday, JACC has confirmed.
The centre of the search zone is 2,200 kilometres north west of Perth, Western Australia, which has become the headquarters for the recovery operation.
Although the search is now in its fifth week, not a single piece of physical evidence has been located to confirm the whereabouts of MH370.
The Bluefin-21 Artemis autonomous underwater vehicle can operate at a depth of 4.5 kilometres and travels at a maximum speed of 4.5 knots, or less than 9 kilometres per hour.
Prime Minister Tony Abbott gave the last indication of the underwater search zone, of about 2000 square kilometres, when speaking to Chinese media on Saturday.
Under optimal conditions the submersible can complete a 25 hour mission if it maintains a speed of 3 knots, according to its manufacturer Bluefin Robotics.
It has been more than a week since the batteries from the flight's two black box beacons was due to expire; and six days since signals consistent with aircraft black box "pings" were last detected.
Abbott said the search was still focused on an area 40km - by - 50km in size. He said search authorities had hoped to reduce the area to within 1km before deploying the Bluefin-21.
Houston stopped short of saying he believed the batteries were dead, but he has previously said the submersible would not be dropped to the ocean floor until there was absolutely no hope the black boxes would emit another signal.
Malaysian Airlines flight MH370, with 239 people on board including two New Zealanders, vanished after mysteriously changing course during a flight from Beijing to Kuala Lumpur on March 8.
It is hoped the plane's two black boxes: a flight data recorder, and a cockpit voice recorder will hold vital information about what happened in those final hours.
Earlier today Malaysian authorities revealed they were uncertain about what to do with the black boxes from Flight MH370 if they were located and brought to the surface.
The country's Attorney-General Abdul Ghani has flown to London to consult with the United Nations Civil Aviation Organisation and other experts about who should get custody of the boxes.
Although Malaysia is the head of the investigation under international law, the government has called on international experts from countries including the United States and Britain to assist with the investigation.
As the suspected final resting place of MH370 falls within Australia's search and rescue zone, Australia has been the lead agency for coordinating the Indian Ocean search effort.