One of the world's foremost wreck hunters believes searchers have found the crash site of the missing Malaysia Airlines jet, and recovering the plane's black boxes is inevitable.

"I think essentially they have found the wreckage site," the director of the UK-based Bluewater Recoveries, David Mearns, told 7.30.

"While the Government hasn't announced that yet, if somebody asked me: 'Technically, do they have enough information to say that?' my answer is unequivocally 'Yes'."

Mr Mearns solved one of the nation's greatest maritime mysteries when he found the wreck of HMAS Sydney deep in the Indian Ocean.

He was awarded an honorary Order of Australia for his work.

His advice was also crucial in helping to find the wreckage of Air France flight 447.

His confidence is based on the strength of the sonar "pings" emitted from the plane's black box recorders.

Those signals appear to have now stopped as the device ran out of battery strength.

Lifeboats from the HMAS Sydney II on the bottom of the ocean not far from the wreck, which was found by director of Bluewater Recoveries David Mearns. ( The Finding Sydney Foundation )

"You just don't hear these signals randomly in the ocean. These are not fleeting sounds - they have got four very, very good detections, with the right spectrum of noise coming from them. It can't be from anything else," Mr Mearns said.

However, he understood why the searchers were being cautious.

The leader of the joint taskforce searching for MH370, Retired Air Chief Marshal Angus Houston, says he will wait to see wreckage before confirming the plane has been found.

"Obviously for the sake of the families and for everybody else they will want photographic proof and that will be coming shortly," Mr Mearns said.

A robotic submarine, the Bluefin21, is already scanning a five-kilometre-by-eight-kilometre area of the seabed - 4,500 metres below the surface of the Indian Ocean.

It was due to stay down for 24 hours, but automatically ascended after just two hours of scanning when it reached its maximum operating depth.

Mr Mearns says he would be surprised if the sonar search turned up anything quickly.

The crew of the HMAS Sydney, which disappeared off the WA coast after a gun battle with the German raider Kormoran on November 19, 1941. ( Supplied: AAP )

He expected it would take weeks, if not months, to recover the black boxes from the Boeing 777.

The plane's cockpit voice recorder and data recorder are separate devices.

He says the real breakthrough in the investigation was made during the analysis of MH370's flight path.

"Somewhere out of some place, fantastic pieces of intelligence were put together to really narrow it down to a small, small area," he said.

"And that's how these guys have been able to find it so quickly.

"The Ocean Shield was out there a couple of days and they got a hit. That has been a tremendous success and miraculous. People were searching for a miracle. This was one."