Another parent Eva, who did not wish to give her surname, was waiting outside the school to pick up their children.
At the scene, she explained she arrived at the school to pick up her daughter who is in Year 9 just before 3pm to find police everywhere.
She said: “It was horrible. Nobody had sent any message.
“I understand this is an emergency but the school hadn’t sent anything.
“I’m waiting to see my daughter who was stuck.”
All pupils are now understoon to have left the school.