Shocking footage of a masked thug threatening High Wycombe school pupils with a knife has emerged online. 

The video, which went viral after it was posted on Instagram and Facebook on January 6, shows a person with their face covered brandishing a knife at terrified pupils wearing Highcrest Academy school uniforms. 

One schoolboy can be seen running into the road to get away and is almost hit by a passing car. 

The video appears to have been filmed by a friend of the thug as pupils from the school, on Hatters Lane, were making their way home. 

The friend can be heard saying: "Don't do it here... there's teachers gonna come, innit." 

One female pupil confronts the knife-wielding thug before pupils can be heard screaming and running away. 

Although the video emerged on social media over the weekend, the incident actually happened on September 7 last year. 

In a letter sent home by Highcrest head teacher, Glen Burke, he reassures concerned parents that the incident did not happen directly outside the gates but in the "vicinity" of the school. 

He said: "[It] was immediately referred to and dealt with by the police. You may recall that I wrote to parents at the time explaining the temporary police presence outside our school.

"I want to reiterate that there have been no further incidents and that the safety of your children will always be paramount to us.

"Indeed, we have senior members of staff on duty at the school gate every morning and every evening."

He said the police attended as a "precautionary measure and as a duty of care to all our students after we reported young men, not in any way associated with The Highcrest Academy, using threatening behaviour in an area close to the school gates." 

A statement from Thames Valley Police said: "We were called to Hatters Lane at just after 3.30pm on September 7 last year to reports that a male was in possession of a knife.

"Police attended the scene but no male was located. Following the report further reassurance patrols were carried out in the area.

"If anyone has any information about the incident they are urged to contact police by calling 101 and quoting reference number 43170266407."