Search crews hunting for missing Malaysia Airlines flight MH370 will deploy a mini-submarine to try to locate the plane's wreckage.

The crew of the British Royal Navy's HMS Echo is working with Australian vessel Ocean Shield to locate the Boeing 777-200's black box flight recorder in the Indian Ocean.

Ocean Shield first picked up two underwater "pings" consistent with those from a black box on 5 April, followed by two more in the same area three days later. Time is precious, since the batteries that power the black box pings could run out at any time.

Phillip Newell, commanding officer of HMS Echo, told Sky News: "We believe we have come close to that point now where we can move to the next stage and deploy a remote vehicle which can go down to the correct depth and search the sea bed."

The crew will use the mini-submarine Bluefin-21 to search the seabed for wreckage. The same device was used to find the Air France plane that crashed into the Atlantic Ocean in 2009.

Malaysia Airlines flight MH370 disappeared on 8 March with 239 people on board and is believed to have crashed in the southern Indian Ocean, around 1,500 miles off the west coast of Australia.

The underwater search zone has been narrowed down to about 500 square miles (1,300 square kilometres).

The Joint Agency Coordination Centre, which is leading international efforts for locate the plane, said 11 military aircraft, one civil aircraft and 14 ships are taking part in Sunday's search.

Australia's Prime Minister Tony Abbott said on Friday: "We are confident that we know the position of the black box flight recorder to within some kilometres.

"But confidence in the approximate position of the black box is not the same as recovering wreckage from almost 4.5km [14,800 feet] beneath the sea."