The submarine being used to search for the wreckage of missing Malaysia flight MH370 had to abort its first mission after reaching its top diving depth.

The multi-million dollar underwater drone, called Bluefin-21, was only designed to work at depths of around 3,500 metres - however the ocean floor in the search zone is around 4,500 metres.

A spokesman for the Joint Agency Coordination Centre (JACC) said "After completing around six hours of its mission, Bluefin-21 exceeded its operating depth limit of 4,500 metres and its built in safety feature returned it to the surface".

"The six hours of data gathered by the Autonomous Underwater Vehicle is currently being extracted and analysed".

It is a blow to the mission which is pinning all hope of finding the missing 777 jet on the success of the submersible. If Bluefin-21 is unable to work at the correct depth it could hinder the search.

After taking two hours to reach the ocean floor it was meant to spend 16 hours searching for wreckage using sonar and a further four hours at the surface downloading the data.

'Likely' black box batteries have expired

Its early return to the monitoring vessel Ocean Shield will be a disappointment to search teams.

The Chief Coordinator of the Joint Agency Coordination Centre, Air Chief Marshal Angus Houston, said it was likely the batteries in MH370's black box had expired and that the submersible was now a "very promising lead" in the search for the plane.

"We haven't had a single detection in six days so I guess it's time to go underwater" he added.

Nine military aircraft, two civil aircraft and 11 ships are involved in today's search for any sign of the Malaysia Airlines jet, which vanished more than five weeks ago during a flight from Kuala Lumpur to Beijing carrying 239 people.

Master Aircrew Andrew Burrow is from the Royal New Zealand Air Force.