Virginia Tech university, scene of the worst school shooting in US history, was on lockdown for several hours on Thursday as police hunted for a man said to have been spotted with a handgun.
Police teams combed the campus for more than five hours looking for the man who was described by three youths attending a camp at the university in Blacksburg, Virginia.
"The campus alert is lifted. There will continue to be a large police presence on campus today," the university said in an update on its website, urging people to remain vigilant.
"Police have not received nor discovered additional information about a person possibly carrying a weapon beyond that reported this morning. The university community may resume normal campus activity."
The scare came four years after 32 people were gunned down and more than 20 others wounded in a horrific shooting spree by a South Korea-born student. The attacker then killed himself.
The university said in a bulletin on its website that at 9:09 am (1309 GMT), the three youths had seen a "white male, six feet (1.83 meters) tall, with light brown hair outside of New Residence Hall East holding what may have been a handgun."
"They say the weapon was covered by a cloth or covering of some sort," the statement said, adding that the suspect was wearing a shirt with blue and white vertical stripes, gray shorts and brown sandals."
Police also released a sketch of the person who was believed to have been carrying a weapon.
White House spokesman Jay Carney said President Barack Obama had "been briefed and will be updated" and that the administration was monitoring events.
"These kinds of situations are frightening regardless," he added. "When it's happening as it is now at Virginia Tech, we're reminded of the horrible and tragic event there in 2007."
The school's assistant vice president Larry Hincker said there were probably several thousand people on campus as summer camps were taking place.
Police had stopped and questioned several people throughout the morning, but no one was found matching the description.
Memories are still fresh here of the 2007 massacre that saw Cho Seung-Hui, a 23-year-old Virginia Tech student, shot to death 32 fellow classmates and teachers before turning the gun on himself.
University officials came under heavy criticism at the time for failing to alert students early enough to the fact that a gunman was loose on campus, after he first shot two students and then a few hours later unleashed a larger shooting spree in a classroom.
The university was fined $55,000 in relation to the April 16, 2007 incident for failing to alert students in time to the gunman.
But student Kelsey Heiter told CNN she had had no hesitation in attending the university despite the shooting.
"It still hits close to home, but at the same time we have received the same kind of updates that we are now... Today, we have a better system. More updated," she said.
"People are receiving news a lot faster than they were then and the good thing is that I have not heard any reported incidents of anyone being hurt or injured or anything of that nature.
"I love Virginia Tech and I wouldn't trade it for anything in the world," she continued, adding that the campus was "very safe."