A 3-year-old girl was flown by medical helicopter to Maine Medical Center in Portland following a single-car crash in Casco at 7 a.m. Thursday.

A 2012 Jeep Compass driven by Ashley McMullen, 23, of Naples, was headed west on Route 302 when it left the road and crashed into a utility pole, then rolled onto its side, according to a news release from Cumberland County Sheriff’s Office Capt. Don Goulet.

The collision broke free the high-tension power lines, which then started a small fire, the release said.

Passers-by put out the fire and helped the people in the car, including a 7-year-old boy, get out, the release said.

McMullen and her son were taken by ambulance to Maine Medical Center with non-life-threatening injuries, the release said.

Her daughter was taken by LifeFlight helicopter to the hospital with a serious head injury.

The younger child was in a car seat and the older one was wearing a seatbelt, the sheriff’s office reported. Nobody was ejected from the car.

The crash is being reconstructed by the sheriff’s office reconstruction team.