Police say a 3-year-old Alabama boy has accidentally shot his 9-year-old sister in the head.

Irondale police Chief Ken Atkinson tells AL.com (http://bit.ly/1nPRJ1B) that the shooting took place Saturday afternoon at their grandparents' house in a Birmingham suburb.

He says the grandfather had left a loaded pistol on a bedroom nightstand, where the boy found it.

Atkinson says the incident seems to be a "tragic accident" but an investigation is underway. Detectives were interviewing other relatives in the home at the time of the shooting.

The girl was flown to Children's of Alabama with life-threatening injuries, AL.com reports.