On Sunday, the event occurred as partygoers made their way towards the city center for Halloween celebrations.
After stabbing people, the suspect, 24, spilled a liquid that looked like oil and lit a fire, according to NHK public television.
“I believed it was a Halloween stunt,” one witness told the Yomiuri newspaper, recounting how other passengers rushed towards his train car in fear. “Then I noticed a man slowly walking this direction, waving a large knife.
“There was blood on the weapon,” he said.
The attacker was arrested on the spot and was being investigated on suspicion of attempted murder. His motive was not immediately known.
It was gathered that a man believed to be in his 60s was unconscious and in critical condition after being stabbed.
Tokyo police officials confirmed that the attack happened inside the Keio train near the Kokuryo station.
The suspect, according to reports, told authorities he “wanted to kill people so he could be sentenced to death”.