Virginia Tech, scene in 2007 of the deadliest shooting at a U.S. college, lifted its campus alert Thursday afternoon after three children attending an academic camp said they saw a man holding an object that looked like a gun covered by a cloth.
The alert instructed students and employees to stay inside and lock their doors and said emergency personnel were responding to the situation.
Officials didn't find anyone but said there would continue to be a large police presence on campus throughout the day.
More than 45,000 people subscribe to the school's alert system, along with an e-mail sent to the entire campus, school spokesman Mark Owczarski said. The school's outdoor sirens also sounded, he said.
All classes were cancelled for the day.