Authorities put Virginia Tech on lockdown Thursday afternoon after three children reported seeing a man holding something that looked like a gun.

The suspected gunman was spotted near the site of the deadly shootings that took place at the university in 2007 and left 33 people dead.

The school posted an update on its website around 1 p.m., saying authorities were combing through buildings on campus. Classes were canceled for the day, and the school said searching the buildings would be a long process

Police swarmed the area, but did not find anyone matching the description.

The university still advised people to stay indoors until further notice.

"We're in a new era. Obviously, this campus experienced something pretty terrible four years ago," said Virginia Tech spokesman Larry Hincker. "And the choice facing us and particularly the police departments are when you get a report, what are you going to do with that report, regardless of what you think the veracity might be."

Federal authorities fined Virginia Tech earlier this year after finding administrators violated campus safety law by waiting more than two hours to notify staff and students during the April massacre.