A woman who was trying to help a stranded motorist on the Red Hill Valley Parkway on Saturday evening was struck by a car and rushed to hospital, police say.

It happened just before 7 p.m., when a 36-year-old woman stopped her car on the west shoulder of the Red Hill near Stone Church Road East in an attempt to help someone stranded in the east side ditch.

While crossing the roadway, the woman was struck by a car being driven by a 39-year-old Hamilton man.

Police say several people tried to help, until paramedics arrived and took the woman to hospital. No one else was hurt.

"Speed does not appear to be a factor in this collision; however the location and the wet road conditions were a factor," a police news release reads.

Hamilton endured an estimated 82 mm of rain since May 1, and roads were slick through most of the weekend.

Police say the woman's injures have been listed as "critical but stable." The collision reconstruction unit is now investigating.