A young girl was critically injured Saturday afternoon, after she was struck by a motorcyclist who allegedly ignored a Mission District stop sign.

According to the San Francisco Police Department, a 49-year-old man riding his motorcycle north on Folsom Street "ran through" the stop sign at Folsom's intersection with 25th Street at 4:22 p.m. Saturday.

When he did that, police say, he struck a 9-year-old girl who was walking in the intersection's crosswalk. The child received a head injury police characterize as "life-threatening" as a result of the collision, and was transported to San Francisco General Hospital for treatment. An update on her condition was not available Monday morning.

The motorcyclist, who remained on the scene, was arrested, police say. As of publication time, his name and the charges he faces had not been released.