Malaysian authorities expanded their search for the missing jetliner westward toward India on Thursday, saying it may have flown for several hours after its last contact with the ground.
That scenario would make finding the Boeing 777 a vastly more difficult task, and raises the possibility that searchers have been looking in the wrong place for the plane and its 239 passengers and crew since it disappeared early Saturday en route to Beijing.
In the latest in a series of false leads in the hunt, search planes were sent on Thursday to search an area off the southern tip of Vietnam where Chinese satellite images published on a Chinese government website reportedly showed three suspected floating objects.
They saw only ocean.
"There is nothing. We went there, there is nothing," said acting Malaysian transport minister Hishammuddin Hussein.
Compounding the frustration, he later said the Chinese Embassy had notified the government that the images were released by mistake and did not show any debris from Malaysia Airlines Flight 370.
The plane left Kuala Lumpur and was flying northeast across the Gulf of Thailand and into the South China Sea when it dropped off civilian radar without any indication it was having any technical problems.
An international search effort is methodically sweeping parts of the South China Sea. A roughly similar-sized hunt is also being conducted to the west in the Strait of Malacca because of military radar sightings that might indicate the plane headed that way after its last contact, passing over the Malay Peninsula. The total area is around 35,800 square miles (92,600 square kilometers), or about the size of Portugal.
The Wall Street Journal newspaper quoted US investigators on Thursday as saying they suspected the plane remained in the air for about four hours after its last confirmed contact, citing data from the plane's engines that are automatically transmitted to the ground as part of a routine maintenance programme.
Hishammuddin said the government had contacted Boeing and Rolls Royce, the engine manufacturer, and both said the last engine data was received at 1:07am, around 23 minutes before the plane's transponders, which identify it to commercial radar and nearby planes, stopped working.
But asked if it were possible that the plane kept flying for several hours, Hishammuddin said: "Of course, we can't rule anything out. This is why we have extended the search. We are expanding our search into the Andaman Sea." The sea, part of the Indian Ocean, is northwest of the Malay Peninsula.
He said Malaysia was asking for radar data from India and other neighboring countries to see if they can trace it flying northwest. India plans to imminently deploy airplanes and ships in the southern section of the sea, a senior Indian official said on condition of anonymity because he was not authorized to speak to the media.
More than two-thirds of those on board the plane were from China, which has shown impatience with the absence of any results. Chinese Premier Li Keqiang told reporters in Beijing on Thursday that it he would like to see better coordination among countries involved in the search.
The passengers' "families and friends are burning with anxiety, the Chinese government and Chinese people are all deeply concerned about their safety," he said at the close of the annual session of the country's legislature. "As long as there is a glimmer of hope we will not stop searching for the plane."
He said China had deployed eight ships and was using 10 satellites to search for the plane.
Investigators have not ruled out any possible cause for the plane's disappearance.
Experts say a massive failure knocking out its electrical systems, while unlikely, could explain why its transponders, which identify it to civilian radar systems and other nearby planes, were not working. Another possibility is that the pilot, or a passenger, likely one with some technical knowledge, switched off the transponders in the hope of flying undetected.
The jet had enough fuel to reach deep into the Indian Ocean.
Malaysia's air force chief said Wednesday that an unidentified object appeared on military radar records about 200 miles (320 kilometers) northwest of Penang, Malaysia, and experts are analyzing the data in an attempt to determine whether the blip is the missing plane.
Malaysia has received some criticism for its handling of the search, in part because it took several days to fully explain why it couldn't state for sure whether the plane had turned back.
Full coverage: Missing Malaysian Airline flight MH370
Officials say they are not hiding anything and are searching areas where the plane is most likely to be, while attempting to establish its actual location.
"There is no real precedent for a situation like this. The plane just vanished," Hishammuddin said.
Experts say that if the plane crashed into the ocean then some debris should be floating on the surface even if most of the jet is submerged. Past experience shows that finding the wreckage can take weeks or even longer, especially if the location of the plane is in doubt.