A Michigan school district put students and parents on alert Thursday after police received multiple reports of an unmarked school bus trying to pick up students.

The superintendent of the Van Buren Public Schools district in Ypsilanti Township, outside of Ann Arbor, said the unmarked yellow bus sped off after a parent who was with a group of students ordered them not to get on board Thursday morning, FOX2 reported.

"Do not allow your students to approach any bus not clearly marked with Van Buren Public Schools on it," a statement on the district’s website said.

The Washtenaw County Sheriff's Office said the suspicious bus appeared to have the lettering on its side painted over.

“It could just be the district made a poor choice to put a bus like that out there, or maybe a charter school, is from a smaller or private school or something like that," Derrick Jackson of the Washtenaw County Sheriff's Office told the station. "We really just don't know at this point and we're just trying to figure out what it is - is it a harmless mistake? Or something more serious?"

Police in nearby Van Buren Township and that school district were notified of the situation.