Virginia Tech university, site of the 2007 shooting that killed 32 people, has been put on lockdown after the possible sighting of a gunman on campus.An alert was issued on the university website at 09:37 (13:37GMT) warning students and staff to stay indoors.
"Person with a gun reported near Dietrick. Stay inside. Secure doors," the school alert said.
There are no reports of any shots having been fired.
In April 2007, Cho Seung-hui shot dead 32 people on a two-and-a-half-hour rampage before killing himself.
Three children attending a camp at the university reported on Thursday morning seeing a white male with brown hair outside New Residence Hall East, holding what "may have been a handgun", Virginia Tech said.
"They [the children] say the weapon was covered by a cloth or covering of some sort. He was walking fast in the direction of the volleyball courts," the statement added.
The group said the man was wearing a blue-and-white striped shirt and sandals.
Police from Virginia Tech and the towns of Blacksburg and Christiansburg are currently searching for the man, the university website said.
No other witnesses have reported seeing the man or anything suspicious