A 14-year-old boy shot dead eight fellow pupils and a security guard and wounded his teacher and six other students when he opened fire in his Belgrade classroom on Wednesday morning, Serbia's interior ministry said.

Milan Milosevic, the father of one of the pupils at the Vladislav Ribnikar elementary school in the Serbian capital, said his daughter was in the class where the gun was fired.

"She managed to escape. [The boy] ... first shot the teacher and then he started shooting randomly," Milosevic told broadcaster N1.

Milan Nedeljkovic, mayor of the central Vracar district where the school is located, said doctors were fighting to save the teacher's life.

The interior ministry statement said eight children and a security guard had been killed and six children had been hospitalized along with the teacher.

Police said a seventh-grade student had been arrested in the schoolyard.

"I saw the security guard lying under the table. I saw two girls with blood on their shirts. They say he (the shooter) was quiet and a good pupil. He recently joined their class," added Milosevic, who had rushed to the school after the shooting.

Officers in helmets and bulletproof vests cordoned off the area around the school.

"I saw kids running out from the school, screaming. Parents came, they were in panic. Later I heard three shots," a girl who attends a high school adjacent to Vladislav Ribnikar told state TV RTS.

Casualties are being treated and an investigation into the motives behind shooting is under way, a police statement said.

Sinisa Ducic, the acting director of a pediatric clinic in Belgrade treating three of the victims said one, a girl, had a head injury and was undergoing surgery.

"She has a serious injury," Ducic told reporters.

Mass shootings are comparatively rare in Serbia, which has very strict gun laws and has issued several amnesties for owners to hand in or register illegal guns.

But the western Balkans are awash with hundreds of thousands of illegal weapons following wars and unrest in the 1990s.

In the deadliest shooting in Serbia since then, Ljubisa Bogdanovic killed 14 people the central village of Velika Ivanca in 2013, while Nikola Radosavljevic killed nine and wounded five in the eastern village of Jabukovac on July 27 2007.

Rade Sefer killed six guests at his son's wedding in the northern town of Senta in 2015 and a year later, Sinisa Zlatic killed five people and wounded twenty-two with an assault rifle in a cafe in the town of Zitiste, also in the north.

All those assailants were adults.