Police operation at Sydney schools ends

A large operation has ended after nine Sydney schools were targeted by phone threats, NSW police say.

Threats have been made to several Sydney high schools, with police operations under way. (AAP)

A large police operation across nine Sydney schools has ended.

Investigations into the sources of a phone threat were continuing, police said.

The schools were placed into "precautionary" lockdown just after midday on Monday as police investigated the threats.

It's the second such incident since the first NSW school term of 2016 began last week.

Seven schools in Sydney and the Illawarra region went into lockdown for several hours last Friday morning following similar threats.

It's understood a few schools, including Sydney Girls High School in the city's east, were evacuated during Monday's operations.

The NSW Department of Education said it worked closely with police during the incident.