UPDATE 2/23/13 10:22 AM EST:
Police have searched the premises and found nothing suspiscious.
Multiple law enforcement agencies had responded to the incident, including State and Cambridge police.
Part of Mass. Ave. was shut down for a period of time. Officers searched the building where the possible gunman was reported, and did not find anything.
There is a person who has been spotted with a long rifle and body armor on the campus of MIT in Cambridge this morning.
According to the Emergency MIT website, the Cambridge police have been notified of the suspicious armed person being in the Main Group building.
The site reports:
This morning information was received from Cambridge Police that there was a person with a long rifle and body armor in the Main Group Building of MIT. Multiple law enforcement agencies have responded. Stay indoors and shelter in place and report suspicious activity to the campus police dispatch at 617 253 1212 or dial 100 from a campus phone. More updates to follow.
There is no word yet on whether any students have been harmed, or if the person has opened fire.
Please keep all of the students and faculty in your prayers!