SAN JOAQUIN COUNTY (CBS13) – Authorities say they suspect DUI was a factor in a deadly crash that has kept Highway 4 west of Stockton closed for most of the day.

The crash happened just before 8 a.m. on the stretch road next to the river at S. Tracy Boulevard.

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According to California Highway Patrol, a semi-truck cross the double yellow lines on Highway 4 and crashed head-on into an SUV heading the opposite direction. The semi then kept on going, sideswiping a minivan, before it finally crashed off the road.

Officers say the SUV driver was killed in the crash. A passenger in the SUV has been flown to a hospital with major injuries.

The driver of the semi suffered moderate injuries, officers say. CHP is investigating the incident as a possible case of DUI.

As of 2:30 p.m., Caltrans says both directions of Highway 4 remain closed due to the crash. A detour is in place.

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The Highway 4 crash was one of two crashes that closed major Delta highways. A crash also blocked Highway 12 through the morning at the Mokelumne River Bridge.