Malaysian police have ruled out involvement of any passengers in the disappearance of a missing jetliner, while Australian officials warned bad weather and a lack of reliable information were impeding efforts to find wreckage from the plane.

Up to 10 planes and nine ships from a half dozen countries yesterday scoured a stretch of the Indian Ocean roughly the size of Britain, where Malaysia Airlines Flight MH370 is believed to have crashed more than three weeks ago.

Authorities have not ruled out mechanical problems as causing the disappearance, but say all the evidence suggests the plane was deliberately diverted from its scheduled route from Kuala Lumpur to Beijing.

Malaysia’s police chief said the investigation was focusing on the cabin crew and pilots, after clearing all 227 passengers of possible involvement in hijacking, sabotage or having personal or psychological problems that could have been connected to the disappearance.

“They have been cleared,” national police chief Khalid Abu Bakar was quoted as saying by state news agency Bernama.

The reality is it’s the most complex and challenging search and rescue operation

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 and without which 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 telemetry 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.