PARK CITY — Park City High School was evacuated when nearly 20 people became sick after a student released pepper spray in or near the school, fire officials said.

Police were called to the school about 2 p.m. on reports of a natural gas leak, Park City fire information officer Tricia Hazelrigg said. Law enforcement officials arrived and confirmed the substance wasn't natural gas but an "unknown substance," she said.

The student later called the school and admitted to releasing pepper spray, Park City Police Capt. Phil Kirk said. He did not immediately know how the pepper spray had gotten into the school's air system.

As of about 4:30 p.m., police hadn't interviewed the student or taken him or her into custody. Additional details about the student were not immediately available.

Nineteen people — including students and faculty members who had been in the school — were treated on scene for respiratory distress. Some who were affected experienced burning in their lungs and abdominal cramping, Hazelrigg said.

Authorities found that some had elevated levels of carbon monoxide in their blood, according to Hazelrigg, but it was not immediately known whether that was related to the pepper spray in the building.

One person was taken to a hospital, Hazelrigg said.

Hazmat crews were investigating Monday afternoon, she said. Initial gas monitor results had showed no signs of explosives or carbon monoxide.

School was out when the incident occurred, Hazelrigg said.

Park City School District spokeswoman Melinda Colton said it was expected the school would remain closed through Monday night and reopen Tuesday morning for classes. Kirk had originally reported the school had reopened within a few hours of the incident.