The hunt for missing Malaysia Airlines Flight MH370 will focus on the southern part of the existing search zone after a new clue to the plane's possible location emerged, Australia said on Thursday.

Fresh information suggested the jet "may have turned south" earlier than thought, Deputy Prime Minister Warren Truss said.

The detail came to light following "further refinement" of satellite data and as investigators attempted to map the plane's position during a failed attempt to contact it earlier in its flight path.

"The search area remains the same, but some of the information that we now have suggests to us that areas a little further to the south -- within the search area, but a little further to the south -- are of particular interest and priority in the search area," he said.

His comments came as Australia and Malaysia inked a memorandum of understanding in Canberra over the next phase of the hunt for the plane, which disappeared on March 8 with 239 people on board en route from Kuala Lumpur to Beijing.

The signing followed a meeting between the two nations and China's Vice-Minister of Transport He Jianzhong.

- Phone call traced -

The plane is believed to have crashed into the southern Indian Ocean far off the west coast of Australia after mysteriously diverting off-course, but a massive air, sea and underwater search has failed to find any wreckage.

Experts have now used technical data to finalise its most likely resting place deep under the Indian Ocean and are preparing for a more intense underwater search, beginning next month.

It will focus on a dauntingly vast stretch of ocean measuring 60,000 square kilometres (23,000 square miles).

Truss said that during efforts to map MH370's location when Malaysia Airlines tried to contact the jet, it was "suggested to us that the aircraft may have turned south a little earlier than we had previously expected".

"After MH370 disappeared from the radar, Malaysia Airlines ground staff sought to make contact using a satellite phone. That was unsuccessful," he said.

"But the detailed research that's being done now has been able to... trace that phone call and help position the aircraft and the direction it was travelling."

The minister said investigators still believed MH370 was somewhere on the search zone's seventh arc, where it emitted a final satellite "handshake".

"It remains on the seventh arc -- that is, there is a very, very strong view that this aircraft will be resting on the seventh arc," he said.

Truss added that ongoing mapping of 87,000 square kilometres of the ocean floor had uncovered "quite remarkable geographical features", including the discovery of new volcanos up to 2,000 metres (6,562 feet) high.

"In one place in particular... the sea depth is as little as 600 metres, and then falls away in just a very short distance to 6,600 metres," he said, indicating the complex task ahead.

Malaysia's Transport Minister Liow Tiong Lai promised to provide "more regular updates and information" about the search when they arise.

Liow, who replaced Hishammuddin Hussein as transport minister in June, added that Malaysia had so far spent about Aus$50 million (US$47 million) on the search and would match Australia's financial commitments in the tender costs for equipment.