The shooting comes less than 48 hours after a 13-year old boy shot dead nine and injured seven at a school in Belgrade before turning himself in.

Interior Minister Bratislav Gasic described the latest shooting as a “terrorist act”, Serbian news portal Telegraf reported, without providing further detail.

According to local media, after a late-night argument in a school yard near Mladenovac, 42 km (26 miles) south of Belgrade, the suspect returned with an assault rifle, opened fire and continued to shoot at people at random from a moving car.

State broadcaster RTS reported a policeman and his sister were among those killed.

Around 600 Serbian police, including elite Special Antiterrorist Unit (SAJ) and Gendarmerie launched a manhunt, dubbed Operation Whirlwind, for a 21-year-old suspect identified only as U.B, RTS reported.

Before dawn, outside the village of Dubona near Mladenovac, a Reuters witness saw heavily armed police establishing a checkpoint and searching incoming traffic.

“It is pitch black here, we are looking for him in this area, taking all precautions, an assault rifle is a serious threat,” a police officer involved in the manhunt said by telephone.

A helicopter, drones and multiple police patrols were also searching for the suspect among the rolling hills and forests around Dubona.

Nation in mourning

N1 TV reported the wounded had been transported to a hospital in Mladenovac and the University Hospital in Belgrade.

The Balkan nation begins three days of official mourning on Friday following its first mass school shooting on Wednesday.

The suspected shooter, a 13-year-old boy, took two of his father’s handguns to kill eight pupils and a security guard in a hallway and history class at their school in the capital Belgrade.

Hundreds of schoolchildren with candles and flowers gathered for a vigil on Thursday evening in streets around the school, while churches planned memorial prayers.

Dozens of high school teachers rallied in front of the Education Ministry in downtown Belgrade on Thursday, demanding improvements to school security and the education system.

Serbia has an entrenched gun culture, especially in rural areas, but also strict gun control laws.

Automatic weapons are illegal and over the years authorities have offered several amnesties to those who surrender them.

Boy shoots dead nine people in Belgrade classroom

After the school shooting in Belgrade, the Serbian government introduced a two-year ban on the issuing of new gun permits, a revision of existing permits and checks on how gun owners store their arms.

Still, the country, and the rest of Western Balkans, are awash with military-grade weapons and ordnance that remained in private hands after the wars of the 1990s.