Eight students and a security guard were killed during a school shooting in the Serbian capital of Belgrade on Wednesday, the interior ministry said, as police arrested a teenage student suspected of carrying out the attack.

The incident rocked the Balkan nation, where there has not been a school shooting of this magnitude in decades.

The shooting occurred at 8:40 am (06:40 GMT) at an elementary school in Belgrade's downtown Vracar district.

Police moved quickly to seal off the neighbourhood, as parents rushed to the scene where students were visibly distraught as they waited outside the school.

"Eight children and a security guard were killed, while six children and one schoolteacher were wounded," the interior ministry said.

"All police forces are still on the ground and are intensively working to shed light on all the facts and circumstances that led to this tragedy."

Milan Nedeljkovic, president of Belgrade's Vracar district where the shooting occurred, said the school's security guard likely prevented more deaths by putting himself in front of the shooter.

The guard "wanted to prevent the tragedy and he was the first victim," Nedeljkovic told reporters told journalists live on television outside the school.

- 'Father's gun' -
Earlier in the morning, police said they had arrested a teenage student following the shooting.

"The police sent all available patrols immediately to the spot and arrested a suspected minor -- a seventh grade student who is suspected of firing several shots from his father's gun in the direction of students and school security," the interior ministry said in a statement.

Police did not release any additional information about the suspected shooter or comment on any possible motive.

"Probably the tragedy would be even bigger if the man did not stand in front of the boy who was shooting," he added.

Astrid Merlini, whose daughter was in the school during the shooting, said teachers moved quickly to hide students as the attack unfolded.

"When (my daughter) saw the security guard fall, she immediately rushed back to class. She was scared. She told her teacher -- there is a shooting upstairs," Merlini told AFP.

"The teacher immediately sheltered the children, locked them in the class."

Gun violence in schools is extremely rare in Serbia, where purchasing a firearm requires a special permit.