OSHKOSH, Wis. (AP) — Authorities say a helicopter hit power lines and crashed into a river in eastern Wisconsin.

The Winnebago County Sheriff's Office says the helicopter crashed into the Fox River Saturday near the Wisconsin Street Bridge in Oshkosh.

Gary Lemiesz, of Oshkosh, told The Oshkosh Northwestern that he watched as a dark green helicopter flew east over the Fox River before turning back and flying west. He says it struck the wires and part of the propeller broke off, after which "it hit hard and sunk."

The Winnebago County Sheriff's Office and Oshkosh police boats are on the scene. The helicopter isn't visible in the water and it's unknown how many people were onboard or what happened to them.

Sheriff's personnel could not be immediately reached for comment.