Children and teachers were unable to leave their school building after a bomb was discovered outside.
Pupils at St Matthews School in Plymouth, Devon, were told to watch a video while they waited for the Royal Navy bomb disposal team to arrive.
A 100m police cordon remained in place for three hours on Wednesday while the squad assessed the suspected WWII mortar, measuring 3in wide.
A controlled explosion is set to be carried out this evening. The Royal Navy bomb disposal team is now on the scene and police said that the device has not been safely disposed of but has been moved.
Children and schoolteachers were initially kept inside the classrooms when the device was found. Some of them were even able to watch Paddington 2 on DVD.
Parents have since been able to collect their children from the school. Some cordons do remain in place.
"The schoolchildren and teachers at St Matthews School are not being allowed to leave," a source told Plymouth Live.
"They are waiting for the bomb disposal team. They are all watching a video until they get the all clear.
"The closure is causing traffic chaos, with buses being delayed due to the incident."
Another source said: "Bomb disposal are on the scene. Children are being kept inside the school, police are waiting for a plan of action."
They added: "I would say there’s about 50 parents and guardians walking down at the moment."
The bomb was found by a digger during construction work within the school grounds, police told the Mirror.
Workmen dug up the war device which was found embedded in the ground and a specialist team from the army evacuated part of the school.
The bomb was reported at 2.30pm and removed by 5.20pm when the cordon was lifted.
One witness told how cars were being turned away which led to traffic delays in the area.
A message from the school to parents had initially said: “All your children are safe. A suspicious device has been unearthed near the school.
“Police have closed the car park. A disposal unit has been called as soon as we know what is happening, we will let you know. Thanks as always for your patience.”
Chris Conners, headteacher, added: “We had information from police early on, they told us what they wanted us to do with the children.
"They were sensible, the children were fantastic. Everyone is safe and I think the roads around have not helped, but the parents were great and staff as well.”
A parent of a child at the school added: “The school has been good and given us updates.
"It was a bit scary when you hear it and have children in school, but they have been good, acted swiftly, and told us not to worry and children were safe.”
Speaking earlier on Wednesday, a Devon and Cornwall Police spokesperson said: "Officers are currently in attendance at Peregrine Road following reports of a suspected mortar, around 3in in size, which has been found.
"There is currently a 100m cordon in place. EOD have been notified and are en route to assess the item."
Mortar bombs were the UK's standard mortar used by the British Army from the early 1930s to the late 1960s.
Used during World War Two, the weapons were initially handicapped by their short range but later improved and used by armies of the British Empire and Commonwealth.
