MANGUM, Okla. (AP) - Authorities are investigating an apparent hit-and-run collision that killed a grandmother and her young granddaughter in southwest Oklahoma.

Mangum police say the collision happened Monday night, just before a thunderstorm moved through the area. Elk City radio station KECO reports that a 59-year-old woman and her 1-year-old granddaughter were walking outside when they were struck and killed by a car. 

No one has been arrested. Authorities say the car drove off the right side of the road, struck multiple vehicles, then hit the woman and her granddaughter.

Authorities say the investigation is ongoing.