A Massachusetts State Police spokesman says one person suspected in the gunfire and explosions has been accounted for and one is at large.
The FBI says it is working with local authorities to determine what happened.
The MIT shooting on the Cambridge campus Thursday night was followed by reports of violence in nearby Watertown, about 10 miles west of Boston.
A state police spokesman said early Friday there is a "strong possibility" the incidents are related.
Cab driver Imran Sais says he heard "a loud boom" while standing on a street corner at a police barricade across from a diner.