The incident happened, authorities report, around 8pm (7am ET) on a train on the Keio railway line, NHK reports.
The train was traveling near Kokuryo Station, in the city of Chofu, west of Tokyo.
It was also reported that the suspect scattered liquid across the wagon, which he then burned.
At least eight people were injured, NHK reported, citing police. One of the victims, a 60-year-old man, was severely injured and unconscious, NHK reports.
Police said they detained a 20-year-old man carrying a knife, NHK reports.
The train operator tweeted that the train had been stopped due to the incident.
It’s a story in development … more is coming.
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