State television said the 34-year-old gunman had also wounded six people, including a police officer, during the shooting in the Medovina neighborhood, The Guardian reported.
The broadcaster RTCG reported that the attacker had randomly shot at people walking in the street, including children.
Four of the wounded were transferred to a hospital in Cetinje, while two others with serious wounds were sent to a clinical centre in the capital, Podgorica, it said.
“When we arrived at the scene, we saw nine dead bodies, including two children, and another two passed away on their way to the hospital,” Andrijana Nastic, a state prosecutor, told Vijesti TV.
Nastic did not say how old the children killed were and could not reveal the identities of the victims.
“I can only say that the shooter was killed by a citizen,” Nastic said. The media had reported earlier that police had killed the shooter.
RTCG quoted police sources as saying the attack came after a family dispute, but gave no further details. Police still have not issued an official statement about the attack, but have blocked off the area.
The Montenegrin Prime Minister, Dritan Abazovic, wrote on his Telegram channel that there had been “an unprecedented tragedy” in Cetinje, calling on the country “to be, in their thoughts, with the families of the innocent victims, their relatives, friends and all the people of Cetinje”.
Residents were left in shock in the shooting’s wake.
“I can’t believe that this happened in Cetinje and Montenegro. I do not know what to say, I am speechless. I do not know where this can lead us,” said Cetinje resident Milorad Mitrovic to RTCG.