Both vehicles caught fire, and the flames spread to brush near the freeway.
Firefighters doused both the vehicles and the brush fires immediately.
One of the cars, a Honda, was sheared in half by the collision.
Three left lanes of the southbound 5 were closed to traffic, while one right lane remained open Monday at about 6 p.m. Traffic was affected.
At least one crash victim was transported to a hospital.
The cause of the collision was under investigation.