Long-range P-8 Poseidon and P-3 Orion surveillance aircraft from the US Navy's 7th Fleet are also involved in the search.
In Manila, 7th fleet commander Vice Admiral Robert Thomas described the combing nature of the search mission as "like mowing the grass", using the planes' high-altitude radars that can spot virtually anything floating on the sea.
"We will continue to cover the areas with airborne assets because that's really what the problem set calls for now," Thomas told reporters aboard the fleet flagship USS Blue Ridge, which was on port call in Manila.
"Right now, we do not have a time frame for the search window. We are just going to keep at it until we're told to stop."
Fleet spokesman Commander William Marks said the surveillance planes had already covered more than 190,000 square km, but emphasised the enormity of the task ahead.
"If you superimpose a map of the United States from the northern part of the Indian Ocean to the southern part of Australia, it is as if we are looking for a few people somewhere between New York and California and we don't know where (they are)," he said.
Apart from the US aircraft, four Australian long-range P-3C Orion maritime surveillance planes and a New Zealand Orion are involved. Young said China had also requested to be involved and that was being considered.
Ships have also been alerted to keep watch, although the vastness of Indian Ocean means very few pass through.
A guided missile destroyer from the US Navy's 7th fleet had been involved in the hunt earlier in the Andaman Sea, but the Pentagon said on Monday it would be withdrawn because the area to be searched was too big.
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Six Australians were on the commercial flight carrying 239 passengers and crew with the majority of those on board either Chinese or Malaysian.
Prime Minister Najib Razak said on Saturday satellite data showed the plane had been deliberately diverted after it lost contact with ground controllers.
Malaysia said on Tuesday it had conferred with the US and Chinese ministers on the search for the Malaysia jet. But intensive background checks of everyone aboard have so far failed to find anyone with a known political or criminal motive to crash or hijack the plane, Western security sources and Chinese authorities said.
China has begun to search for MH370 in Chinese territory, which falls within the northern search corridor, said state news agency Xinhua, and foreign ministry spokesman Hong Lei told a daily news conference that 21 satellites were involved.
"In accordance with Malaysia's request, we are mobilising satellites and radar to search over the Chinese section of the northern corridor which the Malaysians say the plane may have flown over," he said.
Still looking for motive
China's ambassador to Malaysia said his country had carried out a detailed probe into its nationals aboard the flight, which vanished on March 8, and could rule out their involvement.
"The probe into the incident's cause is not suitable to be conducted in a high-profile way," ambassador Huang Huikang told Chinese reporters, state television said on one of its official microblogs.
US and European security sources said efforts by various governments to investigate the backgrounds of everyone on the flight had not, as of Monday, turned up links to militant groups or anything else that could explain the jet's disappearance.
A European diplomat in Kuala Lumpur also said trawls through the passenger manifest had come up blank.
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 on Monday 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.
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Flight MH370 vanished from civilian air traffic control screens off Malaysia's east coast less than an hour after taking off from Kuala Lumpur.
Investigators piecing together patchy data from military radar and satellites believe that someone turned off the aircraft's identifying transponder and ACARS system, which transmits maintenance data, and turned west, crossing the Malay Peninsula and following a commercial aviation route towards India.
Thailand said on Tuesday a re-examination of its military 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.
What happened next is less certain. The plane may have flown for another six hours or more after dropping off Malaysian military radar about 200 miles 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.
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 airport.
Among the items taken for examination was a flight simulator 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.
Full coverage: Malaysian Airlines Flight MH370
"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."
Some US officials have expressed frustration at Malaysia's handling of the investigation. The Malaysian government still had not invited the FBI to send a team to Kuala Lumpur by Monday, two US security officials said.
China has also repeatedly voiced impatience with Malaysia's efforts.
Malaysia's Defence and Acting Transport Minister, Hishammuddin Hussein, told Reuters the country was co-operating with the FBI.
"I have been working with them," he said on Tuesday. "It's up for the FBI to tell us if they need more experts to help because it's not for us to know what they have."
Hishammuddin added that he had spoken to US defense secretary Chuck Hagel and "my counterpart in China" about the search for the plane, now in its 11th fruitless day.