Authorities say the incident happened on a train on the Keio railway line around 8pm (7am ET), the NHK said.
The train operated near the Kokurio train station in Sofu, west of Tokyo.
The suspect is said to have scattered the liquid in the train box and then he set it on fire.
At least eight people were injured, the NHK reported, citing police. One of the victims, a 60-year-old man, was seriously injured and is unconscious, the broadcaster added.
According to the NHK, a 20-year-old man carrying a knife has been arrested, police said.
The train operator said on Twitter that the train was stopped due to the incident.
In August, the Tokyo Fire Department reported that a man had stabbed 10 passengers on a train in Tokyo. The suspect then turned himself in at a convenience store, NHK reported at the time. The Tokyo Metropolitan Police said the man had admitted to “wanting to kill any woman who was happy”, the NHK said.
In June 2008, a man in a small truck drove into a crowd in Tokyo’s famous Akihabara district, then jumped out of a vehicle and started stabbing pedestrians, killing seven people.
Japan – one of the safest countries in the world – strictly controls weapons. According to the US State Department, it is illegal for people to carry pocket knives, craft knives, hunting knives or box cutters in public.
CNN’s Yoko Wakatsuki and Mickey London contributed to the reporting.
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