Calgary police are investigating the shocking assault of a young girl on Monday afternoon.

The girl was attacked in a field near Clarence Sansom Junior High, located in northeast Calgary, Alta.

The victim's age has not been released, but police say the Child Abuse Unit was called in to investigate. The unit focuses on cases of sexual abuse "of children up to but not including 14 years of age at the time of the offence," according to its website.

A teenage boy was arrested and is facing charges.

Eight witnesses have also been taken into custody, but police aren't saying if they were bystanders or had any connection to the incident.

"It's shocking that a sexual assault, if that is what has happened here, occurs to a young person, but to see it happen in a school ground in the middle of the day is certainly extra shocking," Duty Inspector Keith Cain told CTV Calgary.

Police say a teacher saw the assault and reported it from the school.

Investigators have video of the incident and are reviewing it. Unconfirmed media reports suggest it may have been taken by a witness' cell phone.

With files from CTV Calgary