The high school student, whose name was withheld because he is a minor, called police around 1:40 am (1640 GMT Friday) to report he had killed his mother at their home in Kurashiki, Okayama prefecture in western Japan, a local police official told AFP.
When investigators arrived, the woman was lying bleeding in the living room, local media said.
She "had suffered wounds to her head and torso and was transported to a hospital in the city. She was pronounced dead at 2:48 am, and police plan to launch a murder investigation," the police official said, without elaborating further.
Violent crime is still relatively rare in Japan, but several high-profile cases involving young people have heightened public concern.
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