UPDATE 3:58 pm. - Administrators announced that classes will be cancelled for a second day Thursday because of the incident.

In a notice announcing the cancellation, administrators said "project engineers determined that additional shoring is necessary to adequately support portions of the old building."

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Shifting concrete on a school building under construction has forced the school to cancel all classes for about 888 students today.

East Valley school officials said the section of concrete shifted on part of the building that is not occupied right now and is a “significant distance” from classrooms being used for students and staff.

They said they noticed the instability late Tuesday afternoon on the southeast side of the building, which was “exposed due to demolition for the eventual rebuild of our high school.”

District communications director Brittany Kaple said the issue was discovered after students had left campus on Tuesday. She said the district was awaiting feedback from the development teams before determining when school would re-open.

Contractors, engineers and architects are now evaluating the site.

All other East Valley schools are operating on a normal schedule. School athletic activities will take place as planned.

The district said it would provide updates as more information is available today.

This story will be updated.