PHOENIX — A Glendale high school was placed on lockdown temporarily Tuesday morning after an unknown person was reported on campus, but it turned out there was no threat.

The person was determined to be a Mountain Ridge High School student whom a bus driver didn’t recognize, according to a message sent to parents after the lockdown was lifted.

“We will always put the safety of our students and staff first and we thank you for your support towards creating a safe, orderly and caring environment at Mountain Ridge High School,” David Vines, principal of the school on 67th Avenue north of Deer Valley Road, said in the message.

While the lockdown was in effect, the school’s website showed the following message in a pop-up window:

“Mountain Ridge High School is in lockdown. Students and staff are safe. Please do not come to campus. More information to follow.”

It’s not clear when the message was first posted. It was gone by around 9:30 a.m.

Just after 9 a.m., the Glendale Police Department sent an email to the media saying there was no police incident at the school and to contact the Deer Valley Unified School District for information.

Mountain Ridge was one of two schools in the district to experience a disruption Tuesday morning.

Deer Valley High School was evacuated because of smoke in one of the buildings.

The Glendale Fire Department responded to the campus at Union Hills Drive and 51st Avenue and determined there was no fire.

The district said later that the smoke was caused by an issue with an air handler.

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