The car that was being passed on Highway 28 southeast of Wenatchee in Douglas County also was hit in the crash. That driver, Rebeca Niemeyer of Cashmere, Wash., had two children ages 8 and 6 in her car, but they were not hurt, said the WSP.

"An unknown vehicle attempted an unsafe pass while traveling at an excessive speed," the bus company said in a statement

Four people were killed and seven others were injured when a car collided with a passenger bus Sunday in Washington state, authorities said.