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UPDATE 9.51am

The search for missing Malaysia Airlines flight MH370 has intensified to cover an area roughly the size of Australia.

The search area is about 7.68 million square kilometres, Malaysian Transportation Minister Hishammuddin Hussein said, and covers two huge arcs north and south of where last contact was made.

Countries providing satellite and radar information are being sought by Malaysia in locating the plane, Hishammuddin said in a press briefing.

“All effort is being used now to reduce the area of concentration,” he said.

“And that can be done by relooking at satellite data that we already have, seeking assistance from other friends that have satellite capability, radar capability, primary and secondary.”

The search area is divided into the southern corridor that stretches from east Sumatra to the south of the Indian Ocean and the northern corridor that spans from Laos to the Caspian Sea, according to Department of Civil Aviation chief Azharuddin Abul Rahman.

A criminal investigation is looking into hijacking, sabotage, kidnapping, terrorism as well as pilot and co-pilot suicide as possible reasons for the missing plane.

Australia’s role

The Australian Maritime Safety Authority (AMSA) now has responsibility for scouring the Southern Indian Ocean for the plane, which went missing more than a week ago with 239 people on board.

AMSA general manager emergency response division John Young said Australia was working cooperatively with the Malaysian government “to assist with search efforts”.

“The United States and New Zealand will join the Royal Australian Air Force P-3 Orion aircraft in a search effort as a result of a possible route taken by MH370 to an area 3000km south-west of Perth in the southern Indian Ocean,” Mr Young told a press conference.

The search was expected to be difficult.

“The search area is more than 6000 square kilometres.

“This initial search area was developed working with the United States National Transportation Safety Board as a result of work they have already done on behalf of Malaysia.”

AMSA has confirmed two RAAF AP-3C Orion maritime patrol aircraft have conducted two initial sweeps over the southern corridor on Tuesday and while two more aircraft did another sweep later in the day.

A total of four Australian aircraft are active in the area.

“Up to five sorties are expected to be flown on Wednesday using AP-3C, P3-K2 and P-8 aircraft,” an AMSA statement read.

A RAAF servicemen scans the Indian Ocean. Photo: AMSA

Mr Young indicated they attempted to calculate where the aircraft could have entered the water and to where it could have moved.

“The area where the aircraft might have entered the water was then corrected for the water movement and over the lapsed time by the Rescue Coordination Centre in Canberra to provide a possible search area that is relevant to efforts today.”

Prime Minister expresses sympathy

Meanwhile Prime Minister Tony Abbott again expressed his sympathy to the families of the six Australians who were on the flight bound for Beijing that disappeared on March 8.

“We owe it to the people on this ill-fated flight to do what we can to solve this tragic mystery,” he told parliament.

“They remain in our thoughts and prayers at this very difficult time.”

Plane deliberately diverted

Investigators say the Boeing 777 was deliberately diverted during its overnight flight and flew off-course for hours.

They haven’t ruled out hijacking, sabotage, or pilot suicide, and are checking the backgrounds of the 227 passengers and 12 crew members – as well as the ground crew – for personal problems, psychological issues or links to terrorists.

Malaysian Defence Minister Hishammuddin Hussein said on Monday that finding the plane was still the main focus, and he did not rule out that it might be discovered intact.

“The fact that there was no distress signal, no ransom notes, no parties claiming responsibility, there is always hope,” Hishammuddin said at a news conference.

French investigators have arrived in Kuala Lumpur to lend expertise from the two-year search for an Air France jet that crashed in the Atlantic Ocean in 2009.

They said they were able to rely on distress signals in their search. But that vital tool is missing in the Malaysia Airlines case because the flight’s communications were deliberately silenced ahead of its disappearance, investigators say.

“It’s very different from the Air France case. The Malaysian situation is much more difficult,” said Jean Paul Troadec, a special adviser to France’s aviation accident investigation bureau.

Diplomatic efforts

Malaysia’s government sent diplomatic cables to all countries in the search area, seeking more planes and ships, and asking for any radar data that might help.

The search initially focused on seas on either side of Peninsular Malaysia, in the South China Sea and the Straits of Malacca.

It was vastly expanded after Malaysian Prime Minister Najib Razak has said investigators determined that a satellite picked up a faint signal from the aircraft about 7 1/2 hours after takeoff.

The signal indicated the plane would have been somewhere on a vast arc stretching from Kazakhstan in Central Asia to the southern reaches of the Indian Ocean.

#MH370: Malaysia police probe flight engineer who was among the passengers http://t.co/5trliDEi9f pic.twitter.com/CeYjszP4uW

— Hindustan Times (@htTweets) March 17, 2014

Had the plane gone northwest to Central Asia, it would have crossed over countries with busy airspace.

Some experts believe it more likely would have gone south, although Malaysian authorities are not ruling out the northern corridor and are eager for radar data that might confirm or rule out that route.

Search corridors identified by Malaysian authorities. Photo: ABC

Indonesia focused on Indian Ocean waters west of Sumatra, air force spokesman Rear Marshall Hadi Tjahjanto said.

The vast scope of the search, now involving 26 countries, was underlined when a US destroyer that already has helped cover 38,850 square kilometres of water dropped out.

With AAP and ABC