The deadly incident happened as some daily wagers, including children, were loading scrap metals from a container on a truck, Hafiz Rashid Helmandi added, Xinhua reported.
All the injured were shifted to hospital, the official said.
In war-torn and economically impoverished Afghanistan, many children are working on the streets to earn a livelihood and support their families.
Afghanistan has been regarded as the most mine-contaminated countries in the world as mines and unexploded ordnances left over from the war often claim the lives of people, mostly children.
Two children lost their lives and another was seriously wounded in a similar incident in northern Kunduz province some two months ago.