Tokyo police say some of students who were injured in a hammer attack at a local university on Friday told them they were not acquainted with the attacker.

Eight students sustained injuries to their heads or hands when they were attacked during a class at Hosei University's Tama Campus in the city of Machida shortly before 4 p.m..

Police arrested 22-year-old sophomore student Yoo Juhyun, a South Korean national enrolled in the school's Faculty of Social Sciences.

Police say about 10 minutes after the class started, the suspect suddenly stood up and moved from her seat in the third row to the back row. She then began to attack the other students.

The suspect reportedly told investigators she had grown frustrated after being bullied and ignored by her fellow students. She said she earlier found the hammer in another classroom and slipped it into her pocket.

Four of the eight injured students told police they either had no personal acquaintance with the suspect or that they had only been introduced to her.