Malaysian police have ruled out involvement of any passengers in the disappearance of a missing jetliner.

The 227 passengers have been cleared of possible involvement in hijacking, sabotage or having personal or psychological problems that could have been connected to the disappearance.

Malaysia's police chief said the investigation was focusing on the cabin crew and pilots.

Authorities have not ruled out mechanical problems as causing the disappearance.

However, they say all the evidence suggests the plane was deliberately diverted from its scheduled route from Kuala Lumpur to Beijing.

Meanwhile, Australian officials have warned that bad weather and a lack of reliable information were impeding efforts to find wreckage from the plane.

Malaysia Airlines Flight MH370 is believed to have crashed in the Indian Ocean more than three weeks ago.

Up to ten planes and nine ships from a half dozen countries scoured a stretch of the ocean roughly the size of Britain today.

The search and rescue teams are in a race against time to locate the plane's black box recorder, which has an expected battery life of around 30 days.

Without the black box, it may never be possible to find the wreckage.

Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, said that a lack of reliable flight data and punishing conditions at sea were making the operation even more challenging.

"In other words, we don't have a precise aircraft location for six hours before the aircraft went into the water somewhere," he said in an interview with the Australian Broadcasting Corporation.

"The reality is it's the most complex and challenging search and rescue operation, or search and recovery operation now, that I've ever seen."

Broken clouds, sea fog and isolated thunderstorms were expected to further complicate operations, Australia's Joint Agency Coordination Centre said.

The search is now focused on an inhospitable 221, swathe of the southern Indian Ocean about 1,500km (932 miles) west of the Australian city of Perth.

But despite the unprecedented effort, the international team has so far failed to spot any trace of the jetliner.

"Look, it's one of the great mysteries of our time," Australian Prime Minister Tony Abbott said in an interview with local Perth radio station Radio 6iX.

"We owe it to the world, we owe it to those families, to do whatever we reasonably can do (to) get to the bottom of this."

Malaysian Prime Minister Najib Razak is expected to arrive in Perth later today to inspect the search and rescue operations, which are being conducted out of RAAF Base Pearce north of the city.

He is expected to meet Mr Abbott tomorrow.

Mr Najib will arrive with Malaysia coming under fresh fire for its handling of the incident after authorities there changed their account of the plane's critical last communication.

Malaysia yesterday released the full transcript of communications between the Boeing 777 and local air traffic control before it dropped from civilian radar in the early hours of 8 March.

While indicating nothing abnormal, the transcript showed the final words from the cockpit were not the casual "All right, good night" that authorities first reported, but the more standard "Goodnight Malaysian three seven zero".

Minutes after the final radio transmission was received the plane's communications were cut off. It then turned back across Peninsular Malaysia and headed towards the Indian Ocean, according to military radar and limited satellite data.

Malaysian authorities have faced heavy criticism, particularly from China, for mismanaging the search, now in its fourth fruitless week, and holding back information.

Most of the 239 people on board the flight were Chinese.

Among the vessels due to join the search in the coming days is an Australian defence force ship, the Ocean Shield, which has been fitted with a sophisticated US black box locator and an underwater drone.