Eight people were killed and at least 10 were wounded in a shooting in the town of Mladenovac, south of Belgrade, local media reported, with police setting up roadblocks in their hunt for the gunman.
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.
Serbian police launched a manhunt, dubbed Operation Whirlwind, for a 21-year-old suspect identified only as U.B.
According to local media, after an argument near a school in Mladenovac, 42 km (26 miles) south of Belgrade, the suspect came back with an assault rifle, opened fire and continued to shoot at people at random from a moving car.
Near the village of Dubona, not far from Mladenovac, a Reuters witness saw heavily armed police establishing a checkpoint and searching incoming traffic.
A helicopter, drones and multiple police patrols also searched for the suspect among the rolling hills and forests around Dubona.
N1 TV reported the wounded had been transported to a hospital in Mladenovac and the University Hospital in Belgrade.
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.
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.