Police in Sagamihara, Kanagawa Prefecture, have arrested a suspect, Kyodo reported.

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Japanese media said staff called police at 2.30 a.m. local time with reports of a man armed with a knife on the grounds of the Tsukui Yamayuri Garden facility.

A man later went into a police station and said: "I did it."

He is described as a man in his 20s and has been arrested, the media reports said.

The mass killing is coming barely four days after nine people were murdered by some gunmen in a shopping mall in Munich, Germany.