OROVILLE, Calif. (AP/CBS13) — At least three people were killed when ten vehicles collided on Highway 99 near Oroville amid a sea of thick fog early Saturday, the California Highway Patrol said.

The crash involved several big rigs and passenger vehicles and also sent two other people to the hospital with minor to major injuries, authorities said.

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The cause of the crash, which happened just south of Hinamin Drive between Gridley and Biggs, was under investigation, although low visibility due to heavy fog in the area was a contributing factor, the CHP said in a statement.

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While it’s still unclear what caused such a massive crash, what is clear is that it wasn’t easy to see on the road. The National Weather Service says fog blanketed much of the valley overnight, reducing visibility to a quarter-mile.

California Highway Patrol investigators haven’t released the names of the victims nor the number of survivors.

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