Shocking footage has emerged of three teenage girls who have been charged over an alleged bullying incident.

The trio, aged 13, 14 and 15, allegedly attacked a fellow student in the changerooms of a high school in southwest Sydney on February 27.

WATCH THE VIDEO ABOVE: Three teens charged over violent school bullying attack

Know the news with the 7NEWS app: Download today

The footage appears to show the girls forcing their alleged target to bark like a dog while her hair was being pulled.

The distressing footage also appears to show the attackers allegedly shoving the tip of a dirty shoe onto her lips.

The Department of Education said the alleged behaviour was “completely unacceptable and will not be tolerated in NSW public schools”.

“The school is now working closely with NSW Police who are investigating this matter as is appropriate,” the department said.

“Support measures are now in place to ensure the safety and wellbeing of those impacted.”

Footage has emerged of a teenage girl allegedly being bullied by a trio of fellow students. Credit: 7NEWS

Police have since charged the trio with intimidating and assault offences. The 15-year-old will appear before a children’s court on March 18, while the 13 and 14-year-old will appear on April 15.