announced tomorrow would be a day of national mourning.
The 60-year-old, identified as Ljubisa Bogdanovic, shot most of his victims in the head as they slept before trying to kill himself and his wife.
Both were seriously wounded along with a third person, who later died in a hospital, Serbian police chief Milorad Veljovic told reporters at the scene labeling the crime "monstrous."
He said the victims who died -- six men, six women and the child -- include Bogdanovic's mother and his 42-year-old son.
"Twelve people were killed on the spot while the 13th died in hospital," said Veljovic.
According to the victims' neighbours the killed child was a boy. Most of the victims were Bogdanovic's relatives.
The motive for the attack in the village of Velika Ivanca, located about 50 kilometres south of Belgrade, was not immediately clear.
Bogdanovic went house to house at 5:00 am local time (0830 IST) methodically shooting his victims in five houses located on a hill on the outskirts of the village, police said. The houses are only some 10 metres away from each other.
He is thought to have first killed his son and mother, then wounded his wife, before continuing on his spree and turning the gun on himself when a police patrol arrived.
Residents of the village of about 1,700 inhabitants were in shock Tuesday and some wept as they tried to understand the reason behind the killings.
Neighbours said Bogdanovic, who fought as a Serb soldier during the 1990s war in Croatia and had a firearms license, lost his job as a labourer last year. He then became a farmer.
"I had a feeling that I was dreaming. When I woke up I saw my mother, killed at the house's entrance door," Aleksandar Stekic, told reporters.
He was sleeping in another room while his mother was killed and his father was at work.
"I run to the first neighbour and I saw again a killed woman at the entrance ... I was scared I run towards my grand-mother's house but I saw another neighbour killed," the 29-year-old recalled with tears in his eyes.
Police briefly handcuffed him as they suspected he was the perpetrator.