MILLBRAE -- A 16-year-old girl and her 11-year-old brother were in critical condition Tuesday after being struck by a car as they walked across a busy stretch of El Camino Real, police said.

A car hit the siblings, who live in Millbrae, around 10:45 a.m. on the northbound side of the road at Hillcrest Boulevard, said San Mateo County Sheriff's Sgt. Linda Gibbons. The children suffered major injuries and were rushed to San Francisco General Hospital, where they remained Tuesday evening.

Gibbons said the driver is a 21-year-old Redwood City woman who stayed at the crash scene and is cooperating with investigators. It was not immediately clear who was at fault for the collision.

The children, witnesses told investigators, were walking east across El Camino Real in a marked crosswalk. They had almost reached the other side of the road when they were struck by a Honda Accord, police said. There are stop lights at the intersection.

El Camino Real, which celebrated its 100th anniversary Tuesday, is a busy corridor that sees traffic from Highway 101 as well as the nearby Caltrain/BART station.

Sheriff's investigators are working to piece together the crash, said Gibbons. Anyone with information about the collision can call the Sheriff's Office at 650-652-2704.

Contact Joshua Melvin at 650-348-4335.