Virginia Tech, the site of the 2007 mass shooting that killed 33 people, is in lockdown after reports of a man armed with a handgun on campus.
The university issued an alert on its website at 9.37am telling students and employees to stay inside and secure doors.
The alert said the gunman was reported near Dietrick Hall, a three-storey refectory building yards from the dorm where the first shootings took place in the 2007 attack by Seung-Hui Cho.
Virgina Tech said that at 9.09am three young people attending a camp at the university reported seeing a white man with "what may have been a handgun".
The man was described as 6ft, with light brown hair, a blue and white vertically striped shirt, grey shorts and brown sandals. The report said he had no facial hair or glasses. The reported weapon was covered by a cloth or covering of some sort.
The man was reported near New Residence Hall East, walking quickly in the direction of volleyball courts. Staff and agencies responded immediately to the area but found no-one matching the description.