Police say a teenager who opened fire at his school in Serbia’s capital meticulously planned the attack that left eight fellow pupils and a security guard dead.

The shooter, identified as Kosta Kecmanovic, drew sketches of classrooms and wrote a list of children he planned to “liquidate”, according to senior police official Veselin Milic.

The incident at Vladislav Ribnikar school on Wednesday in central Belgrade left six other pupils and one teacher with injuries.

A parent escorts her child following a shooting at a school in the capital Belgrade. Picture: Oliver Bunic/AFP via Getty Images

A father of one pupil said the shooter entered his daughter’s classroom, firing at her teacher and then her classmates as they ducked under their desks. An official said most students were able to flee through a back door.

Mr Milic said Kecmanovic called police himself when the attack was over.

Earlier, police said Kecmanovic was a student at the Vladislav Ribnikar school and was born in 2009. They said he used his father’s gun.

Local media footage showed a commotion as police removed Kecmanovic, whose head was covered as officers led him to a car.

A teenage boy has been arrested after a school shooting in Belgrade. Picture: Oliver Bunic/AFP via Getty Images

Police sealed off the blocks around Vladislav Ribnikar, a primary school whose students would typically range in age from six to 15. Authorities later carried body bags to a waiting van.

Mass shootings are extremely rare in Serbia and in the wider Balkan region; none were reported at schools in recent years. In the last mass shooting, a Balkan war veteran in 2013 killed 13 people in a central Serbian village.

Experts, however, have repeatedly warned of the danger posed by the large number of weapons in the country after the wars of the 1990s.

They also note that decades of instability stemming from the conflicts as well as the ongoing economic hardship could trigger such outbursts.

Police said they received a call about the shooting at around 8:40am local time (7:40am BST) on the first day that classes resumed after a long weekend for the May 1 holiday.

“I was able to hear the shooting. It was non-stop,” said a student who was in a sports class when gunfire erupted elsewhere in the building.

“I didn’t know what was happening. We were receiving some messages on the phone.” The student described the suspect as a “quiet guy” who had good grades.

“He was not so open with everybody – surely I wasn’t expecting this to happen,” she said.

Milan Nedeljkovic, the mayor of the Belgrade area of Vracar where the shooting happened, said that most of the pupils had been taken out a back door of the school.

“We have video surveillance, but now this is a lesson, we need metal detectors too,” he said.

“It is a huge tragedy … something like this [happening] in Belgrade. Such a tragedy at an elementary school.”

Four students and a teacher were sent to University hospital, according to the hospital’s director, who said one child and the teacher were in serious condition.

Milan Milosevic, who said his daughter was in a history class when the shooting took place, told N1 television that he rushed to the school when he heard what had happened. He received a call from his daughter who had gotten out of the building and was unharmed.

“He [the shooter] fired first at the teacher and then the children who ducked under the desks,” Mr Milosevic said his daughter told him.

Serbia shooting: Eight children and guard killed at school as teenager arrested