Search teams hunting for the missing Malaysia Airlines plane have heard the signals again that could be consistent with those emitted by aircraft "black box", even as investigators were racing against time to locate the flight data recorders before its beacons fall silent.

Australian defence vessel Ocean Shield heard the signals again on Tuesday afternoon and evening.

"I can now tell you that Ocean shield has been able to re-aquire the signals on two more occasions," said Air Chief Marshal (retd) Angus Houston, the head of the Joint Agency Coordination Centre (JACC) which is leading the search.

He said the detection on Tuesday afternoon was held for approximately five minutes and 32 seconds and the detection late last night was held for approximately 7 minutes.

The ship had first picked up the underwater pulses on Saturday. But then failed to detect any more pulses.

"I believe we are searching in the right area but we need to visually identify wreckage before we can confirm with certainty that this is the final resting place of MH370," Houston said, adding that these signals will assist in better defining a reduced and much more manageable search area.

"We are not yet at the point to deploying the underwater autonomous water vehicle," he said.

"The better Ocean Shield can define the area, the easier it will be for the autonomous underwater vehicle to subsequently search for aircraft wreckage," he said, adding the new information has narrowed the search area to 75,000 square kilometers.

Houston said work is continuing to refine the search area before a submersible can be sent down to search for wreckage.

Finding the black box is crucial to know what happened on March 8 before the Beijing-bound Malaysia Airlines Boeing 777 flight MH370 with 239 people, including five Indians, disappeared under mysterious circumstances in midair.

The batteries powering the black box are certified to be working for 30 days. Stored in a plane's tail, they are designed to begin sending off distinct, high-pitched signals as soon as they come in contact with water.

Today's search includes up to 11 military planes, four civilian aircraft as well as 14 ships - three of which, Australia's Ocean Shield further north and the British HMS Echo and Chinese Haixun 01 to the south - will be focusing underwater.

The mystery of the missing plane continued to baffle aviation and security authorities who have so far failed to trace the aircraft despite deploying hi-tech radar and other gadgets.