The grandmother of a boy held hostage for a week in an underground bunker in rural Alabama has said the boy is fine physically, but she fears the ordeal could stay with him the rest of his life.

Betty Jean Ransbottom said the boy, who turned six yesterday, seemed fine in hospital after his rescue, but the family was not sure how he was doing mentally.

He was abducted from a school bus last week after 65-year-old Jimmy Lee Dykes shot the driver dead and took the child back to a bunker on his property.

Authorities raided the shelter after realising Dykes had a gun, saying negotiations had deteriorated. Dykes was killed.