WSP: 1-year-old injured when semi-truck hits car on I-5, rolls off hillside (PHOTOS)

SEATTLE -- A 1-year-old baby was one of four people injured when a semi-truck struck a passenger car, flew off Interstate 5 and rolled down a hillside Wednesday near Boeing Field, the Washington State Patrol reported.

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Seattle Fire crews were called to reports of the overturned semi-truck  sometime after 10 a.m. near Boeing Field. Four people were injured when the semi-truck struck a passenger car, causing the semi-truck to roll off the road, WSP said.

A 1-year-old in the passenger car was injured in the crash, but the baby's condition was not immediately known.

A 35-year-old male and a 34-year-old female also in the passenger car suffered minor injuries. The 39-year-old driver of the semi was able to self-extricate himself from the vehicle and declined aid.

The exact cause of the crash is not yet known and Washington State Patrol troopers are investigating.

A 4-mile backup was reported on southbound I-5 following the crash and some lanes of I-5 were closed.