Darwin High School went into lockdown on Friday after a student became “highly upset and agitated”, the school has said.

Principal Jill Hazeldine said in a note to parents – seen by the NT Independent – the student became upset early in the afternoon and that as a precaution the school locked-down while the “incident was de-escalated to ensure the safety of students and staff”.

She did not say what form the agitation had taken or if there had been any injuries.

There were unconfirmed reports that a student or students had attacked a teacher or teachers, but that could not be immediately confirmed on Friday afternoon.

“This is the first time we have had to initiate a lock-down, and everyone quickly responded to the alert in a calm and respectful manner,” Ms Hazeldine wrote.

She added that police and emergency services had “provided adequate care” to the student, and classes resumed again but gave no further details of what happened.