Gunfire and explosions erupted in streets close to the prestigious Massachusetts Institute of Technology on Friday after a police officer was shot dead there, witnesses said.
Local media said one person may have been shot in the incidents as heavily armed police launched a major manhunt following the killing on the MIT campus near Boston.
The explosions and gunfire were heard in the Watertown district north of the university.
Police officers with weapons drawn, and people wearing FBI and ATF jackets could be seen in the live video.
It was not clear if the police activity in Watertown was related to the shooting at MIT, or if either was connected to the bombing of the Boston marathon, which killed three people and wounded 176.
David Procopio, a spokesman for the Massachusetts State Police, said that while he did not believe the MIT shooting was connected to the Boston Marathon bombing, "I can't say that with 100% certainty at this time."
MIT early on Friday said that MIT police had determined that the suspect in the shooting was no longer on campus and it was now safe to resume normal activities.
Massachusetts State Police and Cambridge police said they were assisting in the investigation.
Procopio said the motive for the shooting was not known and the investigation would be led by the Middlesex County District Attorney's Office after the death of the officer.
FBI Boston special agent Greg Comcowich said the office was referring questions about the shooting to Cambridge and MIT police.
"I can tell you that we are aware of it however." The shots on Thursday night were reported near Building 32, MIT said in an emergency statement warning students to "stay indoors and away from the area."
MIT police representatives could not be reached immediately for comment.
"There were blasts, it could have been grenades," local resident Adam Brown told AFP.
The NBC-WJAR channel later showed film of a man lying on the ground in a street in the town and surrounded by police.
Two hours earlier, a gunman shot dead an MIT campus policeman.
MIT is in Cambridge, Massachusetts, just across the Charles River from Boston, where three people were killed and 180 injured in a double bomb attack on the city's marathon on Monday.
Authorities made no immediate link between the two incidents.
(Inputs from Reuters, AFP)
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