In addition to the child killed, at least eight other civilians were injured in the clashes which continued into the night, the emergency services of the Ministry of Health said.
The fighting trapped dozens of families living in the area for hours, said Malek Merset, spokesman for the emergency services. Local media reported that a militia fired at a member of its rivals, wounding a militiaman who was taken to hospital.
The violence was the latest between militias in western Libya. In August, clashes in the capital Tripoli killed more than 30 people, one of the deadliest fighting in Libya for many months.
Libya was thrown into chaos after a NATO-backed uprising toppled and killed longtime dictator Muammar Gaddafi in 2011. The oil-rich county has for years been divided between rival administrations, each backed by rogue militias and foreign governments.
Libya is now shared between two rival administrations. One is that of Prime Minister Abdul Hamid Dbeibah’s government in Tripoli which refused to step down after Libya failed to hold elections last year. A second administration is headed by Prime Minister Fathy Bashagha who operates from the eastern city of Benghazi after unsuccessful efforts to install his government in the capital.