A teacher trained in weapons use has been suspended after accidentally firing his gun in a classroom in California, injuring three students.

Dennis Alexander was teaching a gun safety lesson for his administration of justice class at Seaside high school, near Monterey in northern California, on Tuesday.

The police say the teacher, who also serves as a reserve police officer, was pointing the gun at the ceiling in an attempt to make sure it was not loaded, when the weapon discharged.

Three students were injured by debris, including a 17-year-old whose father told local TV station KSBW that his son was hurt when bullet fragments lodged in his neck.

Alexander was placed on administrative leave both from his teaching job and from the Sand City police department, where he also serves.

The Sand City police chief, Brian Ferrante, told KSBW: “I have concerns about why he was displaying a loaded firearm in a classroom. We will be looking into that.”

Fermin Gonzales, the father of the 17-year-old, said his son was shaken up but OK.

“It’s the craziest thing. It could have been very bad,” Gonzales said.

News of the incident spread further afield on Wednesday, as school students across the country staged walkouts and demonstrations to protest against gun violence and, overwhelmingly, call for greater gun control in the wake of the massacre of 17 students in Florida a month ago.

But while many from the Majory Stoneman Douglas high school in Parkland, Florida, where last month’s mass shooting occurred, have been calling for a ban on assault weapons for civilians, Donald Trump has backed away from early support for greater gun control while promoting a policy of arming teachers in schools.

“I think a lot of questions on parents’ minds are, why a teacher would be pointing a loaded firearm at the ceiling in front of students,” the Monterey Peninsula unified school district superintendent, PK Diffenbaugh, said.

Teachers are not legally allowed to have firearms in California classrooms, even if they have a concealed carry permit, except with explicit authorization, which Alexander did not have, Diffenbaugh said.