An HSC student is under investigation after he was allegedly caught livestreaming an exam on Facebook.

The student, who is understood to attend a western Sydney private school, allegedly filmed the Information Processes and Technology exam from inside the exam room last Tuesday and uploaded the footage to Facebook in real-time.

A teacher appeared to have brought the incident to NESA's attention on social media shortly after the exam finished with this Twitter post.

A Facebook post on Thursday said that he was contacted by the NSW Education Standards Authority, which runs the HSC exams, more than a week after the alleged incident.

The email to the student details the alleged incident and gives him the chance to make a statement.