A 15-year-old student has been tasered and taken into custody after allegedly leaving a classroom armed with a knife at North Sydney Boys High School on Thursday afternoon.

Police said they were called to the Falcon Street campus about 12.40pm following reports a student was carrying a knife after an altercation between two students.

The school was placed into lockdown as officers from North Shore Police Area Command searched for the teenager. He was later found nearby, and police used a taser to subdue him before arresting him.

The student was taken to hospital, and the lockdown was lifted just after 1.30pm.

A NSW Department of Education spokesperson said the lockdown had been enacted as a precaution.

“All students and staff are safe, and students resumed classes after 1.30pm,” the spokesperson said.

Police said investigations into the incident are continuing.

Images: Nine News