The collision involved two passenger vehicles at the 15200 block of Ash Way, Snohomish County Sheriff's Office spokeswoman Shari Ireton said.
The accident was reported at around 3:10 p.m. Friday.
Six people were taken to hospitals, Snohomish County Fire District 1 reported.
One of the drivers was unconscious when firefighters arrived, District 1 spokeswoman Leslie Hynes said. He was transported by paramedics to Harborview Medical Center in Seattle. His passengers, a woman and a man in their 40s, were transported by firefighters to Providence Regional Medical Center Everett.
The driver of the other car was also seriously injured. She was taken by paramedics to Harborview. Her daughters, a toddler and a 13-year-old, had minor injuries and were also transported to Harborview Medical Center.
Ash Way was closed at 156th Avenue and transit buses were rerouted until further notice.
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