A 6-year-old boy has been shot in the head by a 4-year-old in the US state of New Jersey. The younger of the two managed to get hold of a .22 calibre rifle from his family home in Tom's River.

Police are investigating how the younger child obtained the rifle. The older boy is in a serious condition.

Authorities are investigating the incident and are deciding whether anyone should be charged.

Authorities said the children were outside the younger child's home when the shooting happened around 7pm local time. It is not clear if the 4-year-old pulled the trigger or if the rifle accidentally discharged.

The parents of the 4-year-old were home at the time of the incident while the names of the boys have not been released.

The 6-year-old neighbour was taken to hospital with a head wound. Reports say the bullet went through the back of his head and became lodged in his brain.

The investigation is on-going.