A TEENAGE girl is in custody accused of stabbing a classmate in the back with a knife while in class at Renmark High School.

The incident left the Riverland school in lockdown on Tuesday afternoon

The victim, a female student at Renmark High School, is in a serious condition following the incident.

The Education Department said the incident was the result of a “dispute” between an 18-year-old, the alleged attacker, and a younger student aged 17. It was not part of a wider safety issue.

Last night the injured girl was flown to the Royal Adelaide Hospital in a serious but stable condition.

media_camera Police and ambulance officers at the scene of the stabbing at Renmark High School. Picture: Murray Pioneer

Her family kept a bedside vigil as she underwent scans at Riverland General Hospital at Berri before being flown to Adelaide.

An 18-year-old woman from Paringa was last night charged with aggravated assault causing serious harm.

Police said she would also be flown to the Royal Adelaide Hospital “for the treatment of a medical condition”.

She is expected to face a bedside hearing on Wednesday.

The accused girl and the victim are friends on social media.

Authorities were called to the high school at 2.37pm amid reports of a stabbing.

The Advertiser has been told the older girl had hidden the knife up her sleeve before attacking her classmate when she turned her back. Witnesses reported the accused girl had suddenly “snapped” for reasons that remain unclear.

media_camera A letter to parents from Renmark High School following the stabbing of a student at the school today.

It is believed the victim suffered a single stab wound to the middle of her upper back, prompting fears one of her lungs was punctured.

Within minutes of the attack police locked down the school and ordered the students to remain in class as staff and paramedics administered first aid to the victim.

The accused girl was detained at the school as worried parents gathered outside.

Parents said a nearby primary school was also placed in lockdown and students forced to hide under desks.

Renmark High School principal Mat Evans wrote to parents shortly after the attack.

He said students would receive counselling.

“We share your shock at this event which we are treating with the utmost seriousness,” he wrote.

“We are liaising with the Department of Education to ensure the appropriate responses are put in place, including counselling and support for students and staff.”

A department spokesman said the stabbing was triggered by a dispute.

“An assessment is being made as to whether additional security measures are required.” he said.

Acting Superintendent Peter Kennedy told Seven News: “Obviously it’s something that’s going to be of great concern to the students and parents. That’s the focus, getting them the best information we can.”