Authorities say an international land and sea search for a missing Malaysian aircraft is covering an area the size of Australia.
However, a clear motive to explain its disappearance has yet to be established.
Investigators are convinced that someone with a deep knowledge of the Boeing 777-200ER and commercial navigation diverted the jet, carrying 12 crew and 227 passengers, perhaps thousands of miles off course.
Chinese authorities said 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.
Malaysian Acting Transport Minister Hishammuddin Hussein said the "unique, unprecedented" search covered a total area of 2.24 million nautical miles from central Asia to the southern Indian Ocean.
Flight MH370 vanished from civilian air traffic control screens off Malaysia's east coast less than an hour after take-off on 8 March.
Investigators believe that someone turned off the aircraft's identifying transponder and ACARS system that transmits maintenance data.
Families demand answers on missing jet
Chinese families with relatives aboard the missing flight have threatened to go on hunger strike until the Malaysian government tells them the truth about the fate of the aircraft.
Ten days after the airliner vanished, hundreds of family members are still waiting for information in a Beijing hotel.
Around two thirds of the 239 passengers on board flight MH370 are Chinese.
Families vented their pain and anger at Chinese representatives sent by the airline to meet them today and demanded to see the Malaysian ambassador.
Chinese Premier Li Keqiang has asked Malaysian Prime Minister Najib Razak to provide details about the missing flight "in a timely, accurate and comprehensive manner", the official Xinhua news agency reported.
The call followed more than a week's worth of scathing editorials in China's state-run media demanding greater openness from Kuala Lumpur and Malaysia Airlines.
"Unless transparency is ensured, the huge international search operation can never be as fruitful as we hope and expect," read one of several Xinhua commentaries.
"When faced with catastrophe, honesty is human beings' best solution to finding a chance to prevent tragedies happening again," it continued.
Homes of pilot and co-pilot searched
One source familiar with US inquiries said the pilots were being studied because of the technical knowledge needed to disable the aircraft's communications systems.
Malaysian officials said yesterday that suicide by the pilot or co-pilot was a line of inquiry, although they stressed that it was only one of the possibilities under investigation.
Malaysian police have searched the homes of the captain, Zaharie Ahmad Shah, 53, and first officer, Fariq Abdul Hamid, 27, both in middle-class suburbs of Kuala Lumpur close to the international airport.
Among the items taken for examination was a flight simulator Mr Zaharie had built in his home.
A senior police officer with direct knowledge of the investigation said the programs from the pilot's simulator included Indian Ocean runways in the Maldives, Sri Lanka, Diego Garcia and southern India, although he added that US and European runways also featured.
"Generally these flight simulators show hundreds or even thousands of runways," the officer said.
"What we are trying to see is what were the runways that were frequently used. We also need to see what routes the pilot had been assigned to before. This will take time, so people cannot jump the gun just yet."
Thailand today said a re-examination of its military radar data had picked up the plane re-tracing its route across Peninsular Malaysia.
The Thai military had previously said it had not detected any sign of the plane.
The missing plane may have flown for another six hours or more after dropping off Malaysian military radar about 320km northwest of Penang Island.
But the satellite signals that provide the only clues were not intended to work as locators.
The best they can do is place the plane in one of two broad arcs - one stretching from Laos up to the Caspian, the other from west of Indonesia down to the Indian Ocean off Australia - when the last signal was picked up.
Malaysia has asked countries along both corridors, as well as others with satellite capabilities, to re-examine their data to try to narrow the search area.
China, which, with Kazakhstan, is leading the search in the northern corridor, has said it had deployed 21 satellites to scour its territory.
Australia, which is leading the southernmost leg of the search, said it had shrunk its search field based on satellite tracking data and analysis of weather and currents, but that it still covered 600,000sq.km.
"A needle in a haystack remains a good analogy," John Young, general manager of the emergency response division of the Australian Maritime Safety Authority (AMSA), told reporters.