A primary school was placed into "lockdown" after an "unpleasant" email was sent to a number of schools.
Police were seen outside one school after schools in the Manchester and Cheshire reported being sent a threatening email.
Lache Primary School in Chester was placed into lockdown and asked parents to stay away from the school.
Children were not allowed out of the school building and parents were not allowed in.
In a post on Facebook it said: "Do not come to school, we cannot release your child or allow anyone to enter the building.
"These measures are in place to keep your children safe. We will update you as soon as the police have been back in touch."
"There is NOT a threat on site. We have locked down the school to ensure that everyone is safe. Which they are.
"The police are dealing with the situation and are very happy with the measures that we have in place."
Meanwhile Blacon High School said it had put a number of additional measures in to ensure students were safe.
In a statement, Cheshire Police said: "At around 10.05am on Tuesday 12 September, police were made aware of an email which had been sent to a number of schools in Chester and Ellesmere Port which made threats to pupils and staff.
An investigation has been launched and officers have been attending schools to provide reassurance."
Detective Chief Inspector Justin Hancock said: “We would like to reassure parents that this is believed to be malicious and we are doing everything we can to locate the person responsible for these emails."
Chief Inspector Chris Boyd of Greater Manchester Police City of Manchester Division, said: "We take reports of this nature very seriously and whilst we have not advised any schools to close, our officers will nevertheless be stepping up their high-visibility presence around schools at the end of the day today to provide reassurance to them and the wider public."
Lache Primary School added: "Working in conjunction with the police, they would like to reassure parents that this is believed to be a malicious hoax.
"Therefore, we are happy to release the children but this will need to be in a staggered and controlled way for everyone’s safety.
Nursery and Reception -2:30pm
Year 1 and 2 - 2:35pm
Year 3 and 4- 2:40pm
Year 5 and 6- 2:45pm (All must be collected by an adult known to school)
"Normal gates. One way system."