A 5-year-old US boy has been freed unharmed after being held hostage for a week in Alabama by a gunman, who was killed, CNN reports.

Authorities say they will be making a major announcement in the case at a news conference on Monday afternoon in Midland City.

On Monday, an ambulance that had been parked near the scene could be seen driving away.

However, it was not clear if anyone was inside, and the vehicle did not have its sirens or emergency lights on.

CNN cited an unnamed police official as the source that confirmed the report.

Local residents reported hearing gun shots and an explosion.

The kidnapper, Jimmy Lee Dykes, seized the boy, named only as Ethan, on Tuesday as he rode home on a school bus.

Dykes allegedly killed the bus driver who tried to block his access as the rest of the children escaped out the back door.