Emergency personnel responded to a six-car pileup on the northbound 14 Freeway on Monday afternoon near Escondido Canyon Road.
Los Angeles County Fire Inspector Anthony Akins said a car driving on the wrong side of the freeway appears to have caused the crash.
"Several vehicles involved, at least two reported overturned, also with some extrications in progress," Akins said. "It seems like 12 patients is the number we're working with right now. We've also dispatched a helicopter at the request of the incident command staff out there to transport folks to nearby hospitals."
Akins said the injuries range from minor to critical. The accident happened at about 5 p.m.