When responding officers arrived on scene, they found the woman unconscious in the roadway.
According to Huntington Beach Police Lt. Russell Reinhart, the victim may have been walking along the lane closest to the curb and may have stumbled right before the vehicle hit her.
The victim was treated at the scene by paramedics and transported to the UCI Medical Center, where she underwent surgery for serious injuries. Her name wasn't released Thursday.
Several witnesses called police to report the incident, but police say conflicting witness statements are making it difficult to nail down a solid description of the suspect vehicle.
Some witnesses have described the hit-and-run vehicle as an older model white pickup truck.
To make matters more difficult, police said the vehicle may not even have any noticeable damage because the car most likely drove over the victim.
Witnesses are urged to call the Huntington Beach Police Department at (714) 960-8843 or (714) 536-5670.