However,a threatening phone call received by North Sydney Boys High School on Thursday is being treated as a local copycat incident.
The selective boys'high school was evacuated before 10am after the threat was received. A police operation is under way,and no injuries have been reported.
"The police will come down on you heavily,"the Premier warned anyone else considering making a threat against the state's schools.
NSW Police are collaborating with the Australian Federal Police to investigate the overseas threats.
Earlier on Thursday,NSW Police Minister David Elliott warned that the senders of threatening messages would face"the full force of the law".
Mr Elliott told theToday show anyone responsible for the threats could face up to 10 years'in prison.