SYDNEY/KUALA LUMPUR (Reuters), Apr 14 - Australian officials leading the search for a missing Malaysia Airlines plane in the southern Indian Ocean are weighing when to deploy an underwater robot to aid in the hunt, now in its sixth fruitless week.

Malaysia Airlines Flight MH370 disappeared soon after taking off on March 8 from Kuala Lumpur bound for Beijing with 227 passengers and 12 crew on board, triggering a multinational search that is now focused on the Indian Ocean.

Searchers are confident they know the approximate position of wreckage of the Boeing 777, some 1,670 km (1,040 miles) northwest of Perth, after picking up several acoustic signals they believe are from its black box recorders.

With the batteries on the locators now two weeks past their 30-day expected life, the focus may soon shift to trying to find wreckage using sonar and cameras on a small unmanned "robot" known as an Autonomous Underwater Vehicle.

Two ships, one towing a sophisticated "towed pinger locator", are still criss-crossing the zone where four signals or pings were picked up, but the last was almost a week ago.

"This work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed," the Australian agency heading the search said in a statement on Sunday.

The mystery has sparked what is on track to be the most difficult and expensive search and recovery operation in aviation history.

"Trying to locate anything 4.5 kilometres beneath the surface of the ocean about 1,000 kilometres from land is a massive, massive task and it is likely to continue for a long time to come," Australian Prime Minister Tony Abbott said at the weekend.