Avon High School was evacuated just before 3 p.m. on Tuesday after reports of a strange odor, according to the city assistant fire chief.
The assistant fire chief said when crews arrived at the school, they evacuated the building. They found people who were dizzy and disoriented, but not passed out.
School officials reported around 2:20 p.m. Avon police learned from an officer assigned to the high school that there was an unknown irritant found in the school building that was affecting students and teachers.
The irritant was contained to a specific hallway in the building and a small number of students and teachers in the area were having difficulty breathing, officials reported.
Students were dismissed early for the school day. The high school was evacuated and students were escorted to the Avon United Methodist Church where they were picked up by their guardians.
Officials said four students were taken by ambulance to University Hospitals Avon Emergency Center as a precaution.
The assistant fire chief said the odor is not gas. Avon police said the irritant is still unknown. Police will work with high school administration and the Board of Education to attempt to identify the source of the irritant.
Tuesday was the last day of the 2015-2016 school year for senior students.