The Ocean Shield search ship has heard pinging consistent with flight 370's black boxes for over two hours.

The pinger locator deployed by Australia's Ocean Shield defence vessel in the search for missing Malaysia Airlines flight MH370 has detected signals consistent with those emitted by a black box flight recorder.

Retired Air Chief Marshal Angus Houston, who is leading the international search effort, says it is the "most promising lead" so far in the hunt for the plane, which went missing on March 8 with 239 people on board.

However, he has urged caution, saying it could take several days before the signals can be definitely linked to the missing flight.

Air Chief Marshal Houston says a long, consistent underwater signal was picked up for two hours and 20 minutes within "the northern part of the defined search area"

Notice the orange spikes in the center.  Clearly man made, and which give hope that at the very least, the search area has been narrowed down considerably before the boxes run out of power.