Hundreds of pupils were placed in lockdown after their school received a “threatening email” overnight.
Children were not allowed to leave Cardinal Hume Catholic School in Gateshead after the threats were reported to police on Thursday morning.
Northumbria Police said it had received a report of "malicious communications" and some schools had gone into voluntary lockdown as a "precautionary measure” after a number of threats to primary and secondary schools just before 9am.
A force spokesperson told The Independent: "Officers are currently in attendance to carry out enquiries and offer reassurance to the public.
"A decision has been made by some of the schools involved to go into a voluntary lockdown as a precautionary measure."
Detectives are not linking the emails to other threats sent to schools across Birmingham in recent days.
Cardinal Hume School said police had advised parents to not come to the school as increased numbers on site could add to any potential danger.
It is since believed the pupils affected have continued their school days as normal after the threats were deemed not credible.
