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Three girls were killed and a fourth was in critical condition Saturday after the driver of a pickup truck struck members of a Girl Scout troop who were picking up trash on the side of a Wisconsin road, police said.

A woman was also killed in the crash, which occurred about 11:41 a.m. on County Highway P in Lake Hallie, a village in Chippewa County northeast of Eau Claire. The Ford F-150 was traveling north when it crossed over a lane into the ditch, where it struck the group, Lake Hallie police Sgt. Daniel Sokup said.

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The driver, identified as Colton Treu, 21, of Chippewa Falls, fled the scene but later turned himself in, police said. It was not immediately clear what charges he could face. A phone number for Treu could not immediately be found, and it was unclear whether he had an attorney.

"The Lake Hallie Police Department would like to extend our deepest sympathies to the families involved," Sokup said in a statement Saturday evening, adding that the investigation was continuing.

A relative of one of the uninjured girls told the Star-Tribune newspaper of Minneapolis that the children were area Girl Scouts in the fourth grade at Halmstad Elementary School in Chippewa Falls.

They were all wearing bright safety vests and were accompanied by several adults, the relative said.

A cause of the crash was not released by police.

In a statement on Facebook on Saturday evening, Chippewa Falls police called the accident a "truly horrific incident" and extended their condolences.

"Our thoughts and prayers go out to the families, friends, fellow students, fellow scouts and everyone else impacted by this," police said. "Truly, as a community, this affects everyone one of us. Something very precious has been lost and nothing can bring it back. We grieve with you."