The rare and shocking incident prompted panic among parents at the school, many of whom gathered outside the facility and were desperately trying to reach their children.
Seven girls and one boy were killed, alongside the security guard, Belgrade’s Police Chief Veselin Milić said at a press conference.
The suspect opened fire in a history classroom, “because it was near the entrance of the school,” he added. The teenager then called the police himself and waited to be arrested in the schoolyard, Milić said.
A further six children and one teacher have been hospitalized, according to Serbia’s Ministry of Internal Affairs.
The alleged shooter was later filmed being taken from the school in handcuffs with a jacket over his head and wearing blue, skinny jeans. He was flanked by police officers and driven away in an unmarked police car.
But the country has strict gun laws and has issued amnesties for owners to hand in or register illegal firearms, meaning that mass shootings are comparatively rare, according to Reuters.