The victim, who has been recovering from her injuries, has posted about the incident on social media, writing: "I did not know this boy who did this to me."

The girl - who we are not naming - was stabbed during the second period of the day at Thorpe St Andrew School on Wednesday.

The incident is understood to have happened in or near the maths block toilets, after the victim had left her classroom.

Her attacker fled the scene, and the school was put into lockdown, with pupils told to hide and teachers barricading classroom doors shut.

An armed office enters a classroom at the school (Image: Supplied)

Armed officers swarmed the school, searching buildings and surrounding areas.

A 15-year-old boy was arrested on nearby Pound Lane around an hour later.

The girl - who is understood to be a Year 10 pupil, making her 14 or 15 - was taken to hospital for what police described as minor injuries.

She is now believed to be back at home.

In a post on social media, she wrote: "Just to clear things up, I am alive and not dead like people are saying. I did not know this boy who did this to me."

In another post, she wrote: "One minute I’m seeing how my hair looks – next second disaster struck."

A 15-year-old boy was arrested in Pound Lane, near the school, after a short while on the run. (Image: Supplied)

According to reports, the girl was attacked from behind and initially thought she had been punched, before another student saw blood running down her back.

While the school was locked down, around 100 parents arrived at the grounds after hearing the reports on social media, pleading for more information.

The lockdown lasted for around three hours, during which the school bell rang constantly, as pupils and staff remained hidden and in classrooms.

The suspect, who police have described as white British, was arrested on suspicion of causing grievous bodily harm with intent.

Detectives have been given an extra 12 hours to question the boy.

© Eastern Daily Press