KUALA LUMPUR, Malaysia — The search for Flight 370 turned into a criminal investigation on 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.

As part of the investigation, police officers were seen Saturday going to the home of the flight’s pilot, Zaharie Ahmad Shah, in a gated compound, and the Malaysian news media reported that a search had taken place. A spokeswoman for the Royal Malaysia Police would neither confirm nor deny the reports but said there would be a news conference on Sunday.

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.