A man attacked fellow passengers with a knife on a Tokyo commuter train late on Friday, injuring 10.
The suspect, 36, allegedly told police he became angry when he saw women who “looked happy” and wanted to kill them, according to local media reports.
One victim, a female student, is said to be seriously injured, while the others suffered less severe injuries.
Violent crime is rare in Japan and tight security measures are in place in Tokyo, which is hosting the Olympics.
The man attacked passengers on a train near Seijogakuen station at about 20:40 (11:40 BST) on Friday.
The train was brought to an emergency stop by the driver after they heard noises coming from inside the carriages.
According to investigators, the suspect jumped onto the tracks and fled. Train crew guided the passengers along the tracks to the nearest station.