WHEAT RIDGE, Colo. (AP) — Three people were killed Thursday after a semitruck overturned on a highway near Denver and spilled its cargo of plastic pipes, triggering several crashes, police said.

The truck flipped over as it was traveling east on Interstate 70 in Wheat Ridge, a suburb west of Denver, Wheat Ridge police division chief Eric Kellogg said. The large blue pipes went over the median and landed in the westbound lanes, causing crashes involving at least three vehicles, Kellogg said.

The three people killed were in a car with two other passengers who were later hospitalized in stable condition, he said. The truck driver was also taken to the hospital and was in stable condition, he said.

No one in the other vehicles requested medical treatment, Kellogg said.

Why the truck overturned was still being investigated, he said.