The much-talked about US-made Bluefin-21, a robotic mini-submarine designed to map an ocean's seabed and collect data, has been launched to scour the bottom of the Indian Ocean at a depth of 15,000 feet in a last-ditch effort to find the missing Malaysia Airlines MH370 black boxes.

Angus Houston, the head of the search team, announced that the Ocean Shield with the towed pinger locators has ceased its search and given way to the deployment of the underwater vehicle Bluefin-21.

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Houston said that the pinger locators have not picked up any more signals in the past six days and doing an underwater search for the plane is the only way to go now.

Houston said the process of operating the US-made  Bluefin-21 is not easy and it could be slow and painstaking, cautioning that no results are guaranteed.

The mini-sub is equipped with side-scanning sonar and will initially center on 40 square kilometers of seabed near the search area where the detected signals have been picked up.

It will also map the seabed off the waters where the search team has collected two liters of oil slick possibly coming from the missing plane.

Houston said it will take a minimum of 24 hours for each mission to complete. The Bluefin-21 will also narrow down its search near the vicinity of the two liters of oil slicks they have collected.

At least two hours are needed to reach the bottom and while there, another 16 hours will be spent collecting data and producing a high resolution 3D map.

The sub will then surface in another two hours. Another four hours will be allotted to downloading and analyzing data.

Houston cited the difficulties of going down the Indian Ocean, saying that the terrain is "flat and rolling" and has lots of silt at the bottom.

"And if we have silt on the bottom, that can be quite layered, quite deep and that will complicate how things are on the bottom. It's around 4,500 metres," he said.

The Malaysian Airlines MH370 en route to Beijing from Kuala Lumpur with 239 passengers and crew, most of them Chinese, went missing last March 8. Multinational efforts have been exerted in finding the plane but to no avail.

Planes, ships radars and other military assets have been deployed in the search but so far, not a trace of the missing plane has been found.