The incident took place, authorities say, at around 8 p.m. (7 a.m. ET) on a train on the Keio railway line, NHK reported.
The train was operating near Kokuryo Station, in the city of Chofu, west of Tokyo.
The suspect was also reported to have scattered liquid in the train car, which he then set ablaze.
At least eight people were injured, NHK reported citing police. One of the victims, a man in his 60s, is seriously injured and unconscious, the broadcaster added.
Police said a man in his 20s, carrying a knife, has been taken into custody, according to NHK.
The train operator said in a tweet that the train’s operation has been stopped due to the incident.
In August, 10 passengers on a train in Tokyo were stabbed by a man with a knife, according to the Tokyo Fire Department. The suspect later turned himself in at a convenience store, NHK reported at the time. Tokyo Metropolitan Police said the man confessed that he “just wanted to kill any women who looked happy, anyone,” NHK reported.
And in June 2008, a man in a light truck drove into a crowd in Tokyo’s popular Akihabara district and then jumped out of the vehicle and started stabbing pedestrians, killing seven people.
Japan — a country considered one of the safest in the world — strictly regulates weapons. It’s illegal for people to carry a pocket knife, craft knife, hunting knife or box cutter in public, according to the US State Department.
CNN’s Yoko Wakatsuki and Miki Lendon contributed reporting.