SOUTH SAN FRANCISCO -- A 13-year-old boy and his elderly grandmother were both injured Monday morning when the teen attempted to back the woman's vehicle out of the driveway in South San Francisco so he could wash it for her.

The incident occurred around 11:56 a.m. at 707 Fourth Lane, according to police. It was determined that the driver's side door opened while the vehicle was being backed up.

Raquel Rodriguez, 80, was standing just outside the driver's side of the vehicle when it accelerated out of control toward Fourth Lane, police said. Rodriguez was knocked down by the door and the left front wheel rolled over her.

During that time, the teenaged boy fell out of the vehicle, hitting his head on the ground, police said. The vehicle struck the home's metal stair rail and came to rest in the front yard.

Rodriguez was transported to San Francisco General Hospital for a fractured femur, a broken hip and internal injuries and was listed in critical but stable condition.

Police said the boy sustained minor injuries including an abrasion and contusion to his head, legs, ankle and arm.