Malaysia Airlines plane: Area in MH370 search now larger than Australia

The search for the missing Malaysia Airlines plane now encompasses an area stretching 7.7 million square kilometres, larger than the entire land mass of Australia.

An unprecedented search operation involving 26 nations has failed to find any trace of flight MH370, which went missing 11 days ago with 239 passengers on board, including six Australians.

Investigators believe it was diverted by someone with deep knowledge of the Boeing 777-200ER and commercial navigation, and flown perhaps thousands of kilometres off its scheduled course from Kuala Lumpur to Beijing.

"The entire search area is now 2.24 million square nautical miles (7.7 million square kilometres)," Malaysia's acting transport minister Hishammuddin Hussein said in a daily press briefing.

"This is an enormous search area."

Australia has a land mass of about 7.6 million square kilometres.

Investigators believe the plane could have been flown in one of two different directions after its tracking systems were turned off - either north-west into Asia or south-west into the Indian Ocean.

Australia is in charge of the southern Indian Ocean search, which began in an area 3,000 kilometres south-west of Perth early yesterday.

The Australian Maritime Safety Authority (AMSA) says the southern search zone covers 600,000 square kilometres of ocean and has been plotted using data based on the last satellite relay signals sent by the plane.

Australia, New Zealand and US search southern corridor

Aircraft and ships from Australia, New Zealand and the United States are taking part in that search, which represents a narrowing down of the previous Indian Ocean search area.

The size of the search zone mirrors the second area the same distance from the equator in the northern hemisphere.

The southern search currently includes three P-3 Orion aircraft provided by the Royal Australian Air Force, with a fourth to be made available tomorrow.

A New Zealand P-3 Orion and a US P-8 Poseidon are expected to join the search today.

Infographic: A map showing the search zones for missing Malaysia Airlines flight MH370. (Reuters)

One merchant vessel is also searching the area with a further two vessels due to help out.

AMSA's emergency response general manager, John Young, says the search area will be assessed daily.

"We will be moving the search area according to the movement of water and weather influences every day," he said.

"When the aircraft actually get out there and see the real conditions and get experience with the search we will modify our thinking, but at the moment it's a large area with aircraft that are towards the end of their operating limit.

"So they get a short period of time in the search area and that dictates it's going to take quite a long time."

Mr Young says "a needle in a haystack remains a good analogy" and that the search could be ongoing for weeks.

"We are taking this search very seriously. I am describing it as a possibility. The aircraft could have gone north or south," he said.

"Our purpose is firstly to find anyone alive if there is anyone to be found [and] secondly, to prove or discount the possibility that the aircraft came south - to do that would be a significant development in the search."

China has begun searching for the missing jet in its own territory in the possible northern flight corridor, the country's state media said, citing Beijing's envoy in Kuala Lumpur, Huang Huikang.

State media also quoted Mr Huang as saying no evidence had been found linking the 153 Chinese passengers aboard the missing flight to terrorism or hijacking.

Motive remains unclear as Chinese families threaten hunger strike

Police and intelligence agencies have yet to establish a clear motive to explain the plane's disappearance.

Video: Malaysian authorities say search area expanded further (ABC News)

Intensive background checks of everyone aboard have so far failed to find anyone with a known political or criminal motive to hijack or deliberately crash the plane.

Investigators piecing together patchy data from military radar and satellites believe someone turned off the aircraft's identifying transponder and ACARS system, which transmits maintenance data, and turned west, re-crossing the Malay Peninsula and following a commercial aviation route towards India.

Malaysian officials have backtracked on the exact sequence of events - they are now unsure whether the ACARS system was shut down before or after the last radio message was heard from the cockpit - but say that does not make a material difference.

"This does not change our belief, as stated, that up until the point at which it left military primary radar coverage, the aircraft's movements were consistent with deliberate action by someone on the plane," Mr Hishammuddin said.

"That remains the position of the investigating team."

Authorities remain under pressure from desperate relatives of Chinese passengers who have threatened to go on a hunger strike in protest against the lack of information on the search.

Two-thirds of the passengers on the flight were Chinese.

Outside a gathering of families of missing passengers, a woman clutching a placard reading "Respect life. Give us back our families" told reporters the relatives were going on a hunger strike.

"Since they haven't given us the truth about those people's lives, all of us are protesting," the woman said.

"All the relatives are facing mental breakdowns."

Wen Wancheng, whose son was on board the missing flight, said some of the relatives had stopped going to the meetings, given how long they had been waiting for information.

ABC/wires