Published: Aug 04, 2011 4:47 PM EDT
Updated: Aug 04, 2011 3:47 PM EDT

BLACKSBURG, Va.- A lockdown on the Virginia Tech campus has been lifted. Authorities had been searching the campus buildings for a possible gunman.

Three children reported seeing a man holding what looked like a gun this morning and the school sent out an internet alert to the entire campus. For many on the Virginia Tech campus today's developments were an all-too-familiar reminder of the shooting massacre in 2007 that left 33 people dead.    

Thursday afternoon, the university said on its website that the search would be a long process as authorities combed through buildings.

There are 150 major buildings on the campus. Police have released a composite sketch of the person reported earlier in the day by three children attending a summer camp.

Authorities say there have been no further reports of someone with a gun.

"We've alerted the campus, we've given them every piece of information that the police have. Strictly as an abundance of caution, we are going to keep the campus under alert status and ask people to stay indoors until and when the police have made a determination that the alert can be lifted," said Larry Hincker, Associate Vice President of University Relations.  

Federal authorities fined Virginia Tech earlier this year after ruling administrators violated campus safety law in the 2007 massacre. Investigators say back then, the school waited more than two hours to notify staff and students about a potential threat after the first student was shot.