Speaking to the press early Saturday, Prime Minister Najib Razak said the investigation has refocused onto the crew and passengers aboard the missing plane. He added that despite growing evidence to suggest a possible hijacking or sabotage, all possibilities are still being investigated.
WATCH: Malaysian Prime Minister News Conference
The prime minister also said that authorities are now trying to trace the plane across two possible "corridors" -- a northern corridor from northern Thailand through to the border of Kazakstan and Turkmenistan, and a southern corridor from Indonesia to the southern Indian Ocean -- and that search efforts in the South China Sea would be ended.
"Clearly the search for MH370 has entered a new phase," he said. Earlier, a Malaysian government official who is involved in the investigation said investigators have concluded that one of the pilots or someone else with flying experience hijacked the missing Malaysia Airlines jet. The official said no motive has been established, and it is not yet clear where the plane was taken. The official spoke on condition of anonymity because he was not authorized to brief the media.
The official said that hijacking was no longer a theory. "It is conclusive." The Boeing 777's communication with the ground was severed under one hour into a flight March 8 from Kuala Lumpur to Beijing with 239 aboard. Malaysian officials have said radar data suggest it may have turned back and crossed back over the Malaysian peninsula westward, after setting out toward the Chinese capital.
Piracy and pilot suicide have been among the scenarios under study as investigators grew increasingly certain the missing Malaysia Airlines jet reversed course and headed west after its last radio contact with air traffic controllers.
The latest evidence suggests the plane didn't experience a catastrophic incident over the South China Sea as was initially suspected. Some experts had theorized that one of the pilots, or someone else with flying experience, hijacked the plane or committed suicide by plunging the jet into the sea.
A U.S. official said Friday in Washington that investigators were examining the possibility of "human intervention" in the plane's disappearance, adding it may have been "an act of piracy." The official, who wasn't authorized to talk to the media and spoke on condition of anonymity, said it also was possible the plane may have landed somewhere.
The official said key evidence suggesting human intervention was that contact with the Boeing 777's transponder stopped about a dozen minutes before a messaging system on the jet quit. Such a gap would be unlikely in the case of an in-flight catastrophe.
A Malaysian official, who also declined to be identified because he is not authorized to brief the media, said only a skilled aviator could navigate the plane the way it was flown after its last confirmed location over the South China Sea. The official said it had been established with a "more than 50 percent" degree of certainty that military radar had picked up the missing plane after it dropped off civilian radar.
Earlier Malaysia's acting transport minister, Hishammuddin Hussein, had said investigators were still trying to establish with certainty that military radar records of a blip moving west across the Malay Peninsula into the Strait of Malacca showed Flight MH370.
"I will be the most happiest person if we can actually confirm that it is the MH370, then we can move all (search) assets from the South China Sea to the Strait of Malacca," he told reporters. Until then, he said, the international search effort would continue expanding east and west from the plane's last confirmed location.