Lake Macquarie police are appealing for help from the public after a man was seen loitering around the toilet block at Cardiff High School.
Students noticed the man at about 9.30 yesterday morning and notified teachers who called police.
Police are investigating whether it's the same man who exposed himself to school girls in the area in the past couple of weeks.
The man is described as being of a medium build, with an olive/tanned complexion, about 175 cm tall, with dark coloured hair, and unshaven.
He was wearing a grey jumper, black tracksuit pants, and prescription glasses.
Police are urging anyone with information about the man to call Crime Stoppers on 1800 333 000.
