The threat, made on Friday at about 11am, coincided with similar calls to schools in Penrith, Woolooware and Mona Vale.

Lake Illawarra Inspector Matt Glasgow told the Mercury students were evacuated to a nearby oval for about an hour.

They returned a short time ago after an extensive search.

"Nothing adverse was located," Insp Glasgow said. 

Analysts will attempt to trace the call to its source.

"We can't say whether that will be possible or not," Insp Glasgow said. 

Police are liasing with the Department of Education as part of an investigation into the threats. 

They have warned that the threats constitute a serious criminal offence and every effort will be made to identify the person or persons responsible. 

Similar threats were made Pentrith High School in western Sydney and Woolooware High School in the Sutherland Shire, police have confirmed.

Students have been evacuated from the Woolooware school, according to a parent who called 2GB Radio.

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.

with AAP