Another Sydney school targeted by bomb hoax in 'copycat' phone call

Another Sydney school has been evacuated after a "copycat" bomb threat, interrupting HSC exams for the third day in a row in NSW.

North Sydney Boys was the target of a threatening phone call this morning, interrupting 13 students in the middle of their test.

Hundreds of students were forced to leave the school grounds.

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It comes after threatening emails were sent to more than 20 Sydney high schools on Tuesday, and about 10 regional high schools yesterday.

NSW Premier Gladys Berejiklian said this morning the threats sent to schools on Tuesday and Wednesday came from eastern Europe.

"The police Commissioner is working closely with the Australian Federal Police and federal authorities in relation to those threats," Ms Berejiklian said today.

The North Sydney incident was made over the phone, and looks to be a copycat act from someone within Australia, authorities said.