The Kia's passenger, a 59-year-old woman, was also pronounced dead at the scene, police said.
The Ford's two passengers were transported to hospitals, one sustaining internal chest bleeding.
Three passengers in the Kia were moved to hospitals, one of them in critical condition with multiple injuries.
Other passengers were transported to the hospital and had minor injuries, police said.
Alcohol was not a factor in the crash, according to police.
San Diego Police Traffic Division is leading the investigation.
Battalion Chief Flores encouraged San Diegans to take care of themselves this Halloween, reminding residents to be careful on the streets, trick-or-treating or not, especially as it gets darker.
Anyone with information related to the above incident(s) is encouraged to call the police or Crime Stoppers at 888-580-8477.
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