KUALA LUMPUR, Malaysia — The search for Flight 370 turned into a criminal investigation Saturday, after Malaysia declared that the plane had been deliberately diverted and then flown for as long as seven hours toward an unknown point far from its scheduled route of Kuala Lumpur to Beijing.
Prime Minister Najib Razak of Malaysia said Saturday afternoon that he would seek the help of governments across a large expanse of Asia in the search for the Boeing 777, which has been missing for a week and had 239 people on board.
The Malaysian authorities released a map showing that the last satellite signal received from the plane had been sent from a point somewhere along one of two arcs spanning large distances across Asia.
A satellite orbiting 22,250 miles over the middle of the Indian Ocean received the transmission that, based on the angle from which the plane sent it, came from somewhere along one of the two arcs.
One arc runs from the southern border of Kazakhstan in Central Asia to northern Thailand, passing over some hot spots of global insurgency and highly militarized areas. The other arc runs from near Jakarta to the Indian Ocean, roughly 1,000 miles off the west coast of Australia.
The plane changed course after it took off. “These movements are consistent with deliberate action by someone on the plane,” Najib said. He said authorities could not say whether it was a hijacking, and said no motive had been established.
Police on Saturday went to the Kuala Lumpur homes of both the pilot and copilot of the plane, but provided no details on their investigation.
Najib said one communications system had been disabled as the plane flew out over the northeast coast of Malaysia. A second system, a transponder aboard the craft, abruptly stopped broadcasting its location, altitude, speed, and other information at 1:21 a.m., while the plane was a third of the way across the Gulf of Thailand from Malaysia to Vietnam.
Military radar data subsequently showed that the plane turned and flew west across northern Malaysia before arcing out over the wide northern end of the Strait of Malacca, headed at cruising altitude for the Indian Ocean.
The flight had been scheduled to land at 6:30 a.m. in Beijing, so when its last signal was received, at 8:11 a.m., Najib said, it could have been nearly out of fuel.
“The investigation team is making further calculations, which will indicate how far the aircraft may have flown after the last point of contact,” Najib said, reading a statement in English. “Due to the type of satellite data, we are unable to confirm the precise location of the plane when it last made contact with a satellite.”
After Najib’s statement Saturday, the Chinese Ministry of Foreign Affairs demanded to know more, and said that China was sending technical experts to Malaysia. Two-thirds of the people on the jet were Chinese citizens.
A ministry spokesman, Qin Gang, said China would shift its search planes and ships to areas west of Malaysia. That region includes countries that have tense relations with China, including India. Qin said China would seek the cooperation of any countries affected by the redeployment.
China’s foreign minister, Wang Yi, convened ministries and agencies Saturday to discuss the developments. Even with a vastly larger area to search, the officials insisted that the effort must continue with increased vigor.
“The search remains the most pressing and No. 1. task for now,” said an account of the meeting on the ministry website. The officials said the broader search would cover land as well as sea.
In Washington, the Malaysian announcement did little to change American investigators’ perspectives on what happened to the plane.
American investigators have been provided with much of the flight data obtained from radar and satellites, but they say they have far less information about what the Malaysian government has uncovered about the pilots and passengers or the Malaysian inquiry.
Mikael Robertsson, a cofounder of Flightradar24, a global aviation tracking service, said the way the plane’s communications had been shut down pointed to the involvement of someone with considerable aviation expertise and knowledge of the air route, possibly a crew member, willing or unwilling.
The Boeing’s transponder was switched off just as the plane passed from Malaysian to Vietnamese air traffic control space, making it more likely that the plane’s absence from communications would not arouse attention, Robertsson said by telephone from Sweden.
“Always when you fly, you are in contact with air traffic control in some country,” he said. “Instead of contacting the Vietnam air traffic control, the transponder signal was turned off, so I think the timing of turning off the signal just after you have left Malaysian air traffic control indicates someone did this on purpose, and he found the perfect moment when he wasn’t in control by Malaysia or Vietnam.’’