Police are investigating the unexplained death of a nine-year-old boy at his home at Raetihi, north of Wanganui, today.

"A family member discovered the boy was deceased and notified police and ambulance,'' Detective Senior Sergeant Keith Borrell said.

"We hope to have a post-mortem completed by late this evening. At this stage the cause of death remains unexplained.''

Police were interviewing witnesses and a scene examination was underway.