23 people, most of them students, were injured after an unknown substance was sprayed at a junior high school in Kaizuka City, Osaka Prefecture, western Japan, on Friday morning.

According to the city's board of education, 15 students and eight school staff members, including teachers, complained of throat irritation and skin rashes after the incident, reported by Japan's Jiji Press news agency. The reports did not indicate any serious injuries.

After Osaka police arrived at the scene, they detained a second-year junior high school student outside the school building.

Sources said the boy admitted to spraying the substance and that police will question him on suspicion of causing injuries to others.