Watertown — Police have converged on a neighbourhood outside Boston where there were reports of explosives being detonated and police are telling reporters to turn off their cell phones, as a second arrest was set to be made, say reports.
Dozens of officers and National Guard members are in Watertown, where television outlets report that gunfire and explosions have been heard. A helicopter is circling overhead, the AP reported on Friday.
Authorities early on Friday were calling for somebody to get on the ground and put their hands up and a loud thud was heard after someone shouted "fire in the hole".
Reporters are being told to move away from the scene. A police officer told a reporter: "If you want to live, turn off your cell phone."
Earlier on Thursday night a campus police officer was shot and killed at MIT and authorities were searching for the person responsible.
The Boston Globe reported that during a car chase that ensued after the police officer was killed, explosives were thrown at police by the suspects. The report said the suspects had reportedly stolen a black Mercedes from Cambridge, but ended up being caught in Watertown.
MIT police were sweeping the campus early on Friday, according to a campus alert. Massachusetts State Police and Cambridge police said they were assisting in the investigation.
David Procopio, a spokesperson for the Massachusetts State Police, 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.
The shooting in Cambridge occurred as nerves were on edge in neighbouring Boston, where two bombs exploded on Monday at the finish line of the city's famed marathon, killing three people and wounding 176.
Procopio said that while he did not believe the shooting was connected to the Boston Marathon bombing, "I can't say that with 100% certainty at this time."
State Police were assisting in the search for suspects, Procopio said in a statement.
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.