THE search for Malaysian Airlines Flight MH370 is set to shift to the vast depths of the Indian Ocean.

The Australian vessel Ocean Shield will stop seeking pings today and the autonomous underwater vehicle (AUV) Bluefin-21 will be deployed this evening to search the ocean floor, search co-ordinator Angus Houston has announced.

Crews are also to investigate an oil slick close to the search area, he added.

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The Bluefin 21 autonomous sub can create a 3D sonar map of the area to chart any debris on the seafloor.

Retired defence chief Air Chief Marshal Houston told a media conference in Perth that the chances of any floating material from MH370 being recovered from the ocean has greatly diminished.

“We haven’t had a single detection in six days - it’s time to go under water,” he said.

“The deployment of the autonomous underwater vehicle has the potential to take us a further step towards visual identification since it offers a possible opportunity to detect debris from the aircraft on the ocean floor,” he said.

Any hope of receiving further “pings’’ from the devices is highly unlikely due to battery exhaustion, Air Chief Marshal Houston said.

“We’ve got a very good lead - we’ve just got to wait and see if Bluefin-21 can find the wreckage,” he said.

But he warned there was still no further certainty as to whether the area was MH370’s final resting place.

“I would caution you against raising hopes that the deployment of the autonomous underwater vehicle will result in the detection of the aircraft wreckage. It may not.”

Air Chief Marshal Houston said the search area “is new to man” and may have a lot of silt.

He said Ocean Shield had also detected an oil slick downwind from the search area and a sample will be tested.

“Aircraft wreckage needs to be visually recognised before we can say this is the final resting place of MH370,” Air Chief Marshal Houston said.

The remote underwater vehicle will be deployed this evening in the search area based on the last emissions from the locator beacons of the aircraft’s black boxes, Air Chief Marshal Houston said.

Bluefin-21’s missions will each take a minimum of 24 hours, with the first to cover an area of 40 square kilometres.

“We anticipate deploying it this evening,” he said. “It will be deployed again exactly 24 hours after the first delployment.”

Air Chief Marshal Houston said a decision will soon have to be made about whether to continue looking for debris on the surface.

“The air and surface search for floating material will be completed in the next two to three days in the area where the aircraft most likely entered the water,” he said.

“The chances of any floating material being recovered have greatly diminished and it will be appropriate to confer with Australia’s partners to decide the way ahead later this week.”

Air Chief Marshal Houston said other vehicles, which can go deeper than 4,500 metres, are being looked at in case Bluefin-21 isn’t capable of reaching the necessary level.

“Those sorts of possibilities … are being looked at as we speak. But a lot will depend on the outcome of what we find when we go down and take a look.”

The co-ordinator conceded the search was “very expensive” and countries involved are “running up big costs”.

“I think the world community should be very appreciative to those countries for their contribution to what I would say is one of the largest search and rescue, search and recovery operations that I’ve seen in my lifetime.”

The search area has been narrowed down to patch of ocean floor less than 1000 kilometres square making a successful physical search almost impossible.

The Bluefin-21 will submerge to its near maximum depth of 4500 metres and conduct 20-hour long sweeps using powerful sonars.

If any wreckage is found the sonars will be switched to cameras to and lights to record whatever lies on the bottom.

The initial search will focus on the location of the strongest “pings’’ detected last week by the Ocean Shield.