Transport Minister Hishammuddin Hussein: "At this stage both the northern and southern corridors are being treated with equal importance". Photo: BBC NEWS

The search area - from central Asia to the southern Indian Ocean - takes in large tracts of land and sea.

An already complex search operation has become even more difficult, Malaysia's transport minister says.

Crew, passengers and ground staff are being investigated after it was confirmed the jet was commandeered.

Investigators are trying to obtain more radar and satellite data from any of the countries that Malaysia Airlines flight MH370 may have passed over, with its 239 crew and passengers.

The leaders of several Asian countries have been briefed by the Malaysia government in what Transport Minister Hishammuddin Hussein has described as a new phase of the search.

"From focusing mainly on shallow seas, we are now looking at large tracts of land, crossing 11 countries, as well as deep and remote oceans," he said at a news conference.

Malaysian officials are contacting countries including Kazakhstan, Uzbekistan, Kyrgyzstan, Turkmenistan, Pakistan, Bangladesh, India, China, Myanmar, Laos, Vietnam, Thailand, Indonesia, Australia and France.

They are also asking countries to provide assistance in the search for the plane, including satellite data and analysis, ground-search capabilities, and maritime and air assets.

National police chief Gen Khalid Abu Bakar said background checks had been requested on all passengers aboard the plane, but that so far nothing suspicious had been reported - though some intelligence agencies still had to respond.

The police are also reportedly looking at the family life and psychological state of the plane's pilot, Zaharie Shah, and co-pilot Fariq Abdul Hamid, and searched their homes on Saturday.

The two men had not asked to fly together, Mr Hishammuddin confirmed at the news conference.

Officers spoke to relatives of the pilot and experts are examining the pilot's personal flight simulator. Police have visited his house for a second day.

Those who know Mr Zaharie, 53, insist he is a normal family man, reports the BBC's Jonah Fisher in Kuala Lumpur.

With 18,000 hours of flying experience, he is a self-confessed "aviation geek" and proudly posted pictures online of the flight simulator he built at home.

As well as the crew and passengers, police are investigating the engineers and other ground staff who may have had contact with the aircraft before take-off.

It has also emerged that a team from British telecommunications company Inmarsat team arrived on Saturday in Malaysia.

An Inmarsat satellite is said have continued receiving signals from flight MH370 at least five hours after the plane was reported lost.

A team of French investigators is to travel to Malaysia on Monday to help with the search, the French transport ministry has said in a statement. They will join members of the US National Transportation Safety Board already in Malaysia.

Malaysian Prime Minister Najib Razak announced on Saturday that the plane's communication systems had been deliberately cut before it was diverted from its route.

According to satellite evidence, the Boeing 777 could have continued flying for a further seven hours after its last radar contact, he said.

The flight left Kuala Lumpur for Beijing at 00:40 local time (16:40 GMT) on 8 March and disappeared off air traffic controllers' screens at about 01:20.

An extensive search - involving 43 ships and 58 aircraft - since the plane disappeared has proved fruitless.