Threatening phone calls to at least 15 schools in NSW and Victoria have caused schools to be evacuated and disrupted thousands of students in the first week of term.

A series of phone calls made about 11am on Friday, including one reportedly using a computerised voice, prompted the schools to call police.

Victoria Police said it was trying to find the origin of the calls but did not have any reason to think they were terrorism-related.

Sale Primary School in eastern Victoria shut soon after receiving a call and moved students to a nearby high school to be picked up.

"Like all schools, we have an emergency management plan in place for situations like this, and we practise these throughout the year," principal Brad Evans said in a statement to parents.

An investigation is also under way in NSW after seven schools, including five in Sydney, were evacuated.

"Making such threats is a serious criminal offence and every effort will be made to identify the person or persons responsible," NSW Police said in a statement.

The NSW Department of Education and Victorian Education Department issued statements saying the schools were taking precautionary measures, including evacuations, to ensure the safety of students.

Neither Victoria Police nor NSW Police would comment on reports that a group of anonymous Russian hackers were involved in the spate of threats.

"NSW Police is investigating the matter and it is too early to provide any further comment at this stage," a spokeswoman told AAP.

AREAS AFFECTED:

- Victoria: Berwick, Craigieburn, Reservoir, Wonthaggi, Cowes (Phillip Island), Sale, Morwell, Lakes Entrance.

- NSW: Penrith, Richmond, Mona Vale, Ambarvale, Woolooware, Ulladulla, Lake Illawarra.