The police department in Henrico County said on Twitter that officers were on scene at the Academy at Virginia Randolph, a school located in Glen Allen, close to Richmond.
There are currently no reported injuries and no confirmed reports of gun fire, according to the department.
"Call 911 (text if you can’t) in case of emergency," police advised on social media.
A spokesperson for Henrico County Public Schools said police are going door to door on the school campus and conducting a check.
"So far no one's been hurt, and there's no evidence that a weapon's been used," spokesperson Andy Jenks said.
School officials are planning on dismissing students "the same way they got here, which would mean on their bus, or perhaps in a car", Jenks added in his statement.
A family reunification area has been set up for students to meet up with their relatives.