Two HSC exams at the academically-selective North Sydney Boys High School have been moved to a different venue after a threatening phone call prompted a campus evacuation.
Premier Gladys Berejiklian confirmed a person rang the high school at Crows Nest on Thursday morning saying there was a bomb on campus, forcing the school to evacuate before HSC students were due to sit their modern history exam.
It's the third day of this year's HSC calendar in which a bomb hoax has disrupted exams.
The NSW Education Standards Authority said North Sydney Boys' modern history exam and French extension exam would be moved to another venue.
The history exam would start later than scheduled, but students would still have 185 minutes to complete the exam, while the two-hour French exam would start at 2pm as scheduled.
There were 15 students in total affected by Thursday's bomb hoax.
"NESA has rigorous and longstanding processes to make sure students affected by misadventure get a fair result," the authority said in a statement.
The incident comes after threatening emails were on Tuesday sent to about 20 Sydney schools and some regional schools were on Wednesday evacuated.
Ms Berejiklian said NSW police had sourced Tuesday and Wednesday's hoaxes to eastern Europe and were working with their federal counterparts.
But Thursday's hoax was believed to be a "copycat" offender, using a local number.
"I have confidence that the police and the education department will resolve what is in the best interest of every student," Ms Berejiklian said.
NESA said no affected student would be required to re-sit an exam.