SYDNEY (AFP) - Australian Prime Minister Tony Abbott said on Friday he was "very confident" that signals detected in the search for missing Malaysia Airlines Flight MH370 were from the aircraft's black box.

"We have very much narrowed down the search area and we are very confident the signals are from the black box," Mr Abbott said from China, the Australian Broadcasting Corporation reported.

The logging of a fifth signal on Friday spurred the hunt for missing Malaysian airliner MH370 as search crews work round-the-clock to find elusive wreckage in the southern Indian Ocean.

The Australian-led operation out of a Perth airbase is racing to gather as many signals as possible to determine an exact resting place for the Boeing 777 before sending down a submersible to plumb the depths.

The ping-emitting beacons on Flight MH370's data and cockpit voice recorders are expected to fade, more than a month after the plane, which was carrying 227 passengers and 12 crew, vanished on March 8 and flew thousands of kilometres off its Kuala Lumpur-to-Beijing route.