Threats have been made to several NSW high schools, with police operations underway at at least three Sydney schools.
Officers are at Penrith High School in the west, Woolooware High School in the Sutherland Shire, and an Ambarvale school in the city's southwest, police confirmed on Friday.
Police could not confirm how many schools, which have just reopened after the summer holiday, had been put in lockdown.
But they said threats had been made to schools in the Metropolitan and Southern Regions.
"Making such threats is a serious criminal offence and every effort will be made to identify the person or persons responsible," police said in a statement.
Video footage from the Seven Network shows students and teachers from Penrith High School gathered at a sporting ground.
Schools in Ulladulla, Richmond and Mona Vale have also been affected, according to the Seven Network.
A mother of a student at Woolooware school told 2GB Radio her daughter had been evacuated from her school because of bomb threats.
The Department of Education released a statement saying it has been working closely with police following threats.
"Each school is taking precautionary measures to ensure the safety of its students and no students are in danger," a spokesman said on Friday.
Police have been going to each school as a precaution, he said.
It follows phone call threats to Victorian schools, which have been evacuated, and similar calls at overseas schools in the past 24 hours.
Fairfax Media is reporting Berwick Chase Primary in Berwick and Aitken Creek Primary School in Craigieburn are among the schools that have been evacuated.
Prime 7 Gippsland reported schools in the eastern Victorian towns of Sale, Traralgon and Lakes Entrance have also been evacuated.