Students in Melbourne's southeast spent almost three quarters of an hour cowered in classrooms when a 15-year-old sparked a lockdown by taking a toy gun to a school yesterday.

Police were called to the school before noon and a 15-year-old boy was arrested for possessing an imitation firearm.

The boy was charged with possessing a prohibited weapon and bailed to appear at a children’s court at a later date.

A loudspeaker notification alerted teachers and students to the incident about 11.40am Wednesday morning.

Teachers told students to stay in their classrooms and told them they were not allowed to use their phones during the 40-minute incident.

A scared student told the Herald Sun they were told to hide behind their desk in the classroom while people walked around.

“Students were freaking out,” the student said.

“We locked the doors, turned off the lights, hid behind the desks and the blinds were pulled down.

“We heard people walking around locking doors and we heard sirens. There were a lot of rumours going around.”

The teenage student wanted to remain anonymous because school staff told students they were not allowed to speak to media in a post-lockdown assembly.

They were not told what sparked the late-morning chaos, nor that a teenage boy had been arrested by police, despite a police presence at the school.

They were allegedly offered counselling if they were feeling upset.

Last night the teenage boy was assisting police with their inquiries.

The police investigation into the incident is ongoing.

Staff at the high school followed safety protocols and the issue was handled calmly, according to the principal.

“Our safety culture was clearly evident today when a potential safety risk was raised with members of staff,” the principal said in a statement provided to the Herald Sun.

“Staff responded as they had been trained, and the matter was addressed in a very calm manner.”

The school confirmed no students or staff were in danger and that support services were made available.

tamsin.rose@news.com.au