A teenager is in custody after allegedly firing multiple shots from a rifle at his former school, hitting a building and forcing students into lockdown.
It's understood to be the first firearms incident at a West Australian school.
Police responded to reports of gunfire at Atlantis Beach Baptist College on Wednesday about 11.50am.
"At the scene, police took into custody a 15-year-old male," Commissioner Col Blanch told reporters after the incident.
"We believe at this stage ... he was acting alone."
The boy, understood to be a former student of the private school, is alleged to have fired three shots from the car park.
"The bullet did penetrate the building and through into the inside," Mr Blanch said.
"We believe there were people in the building, we don't know how many."
Officers seized two rifles after the incident from a nearby black four-wheel drive vehicle, understood to belong to the boy's father, the teen allegedly arrived at the scene in.
They also found three bullet shells believed to have been discharged from the weapons the boy allegedly fired.
"(He) is now still in custody and assisting police with their inquiries," the commissioner said.
"There is no further threat to the community.
"Everyone is safe and there have been no injuries."
The weapons, a .243 and .22 calibre, were licensed to the boy's home and believed to be registered to his father, Mr Blanch said.
"We will look into every aspect during this investigation to understand how a 15-year-old person is allegedly in possession of two long-arm rifles and has shot into a school in these terrible circumstances," he said.
The commissioner described the incident as a rare and shocking incident.
"These poor kids ... It was the unknown for those kids, they didn't know what they were facing, the teachers didn't know what they were facing," he said.
"It really shocked me that this has occurred in WA.
"As police commissioner, I've never seen anything like it."
Detectives continue to investigate the shooting, with the teen's parents yet to be interviewed.
"Again, how does a 15-year-old get hold of two lethal weapons and fire them in a school area," Mr Blanch said.
The school was placed in lockdown during the incident.
Mr Blanch did not know how long the boy spent in the school before police received a triple-zero call alerting them to the shooting.
It is not known when the boy was a student at the school and the circumstances under which he left.
Police have commended the school's staff and students for the information they provided as the shooting unfolded, including a 12-year-old student.
"They rang triple-zero and they provided excellent credible information that allowed our officers to respond appropriately," the commissioner said.
"I really do want to thank the teachers and students who enacted those protocols and helped police make a safe arrest."
Atlantis Beach Baptist College is a co-educational school for boys and girls that started in 2017.
It is located in the suburb of Two Rocks about 70km north of Perth.
