An 8-year-old Florida boy was accidentally shot when a burn barrel with guns inside was set on Kacper Sobieskifire, authorities said.

The boy was cleaning up a backyard with his grandmother and other children at the time of the Monday incident, the Jacksonville Sheriff's Office said.

A burn barrel was filled with yard waste and then set on fire, authorities said. But two guns were under the debris in the burn barrel, and a shot went off while the boy was standing next to the barrel, according to the sheriff's office.

The boy's family heard two more shots as they rushed him to the hospital, authorities said.

The 8-year-old suffered a through-and-through gunshot to his lower leg and was hospitalized with non-life-threatening injuries, authorities said.

The incident "appears to be accidental and negligent," the sheriff's office said.