A police officer shot on the campus at the Massachusetts Institute of Technology has died from injuries.
Cambridge police and the Middlesex District Attorney’s office said the officer was responding to a report of a disturbance when he was shot multiple times.
He later died in hospital, and his name was not immediately released.
State police spokesman Dave Procopio said the shooting took place about 10.30pm local time outside an MIT building.
He said the authorities are searching for a suspect or suspects, and no arrests have been made.
MIT police, Cambridge police and state police are involved in the investigation.
About 11,000 people attend the prestigious school outside Boston.
The campus website said police were sweeping the campus and urged people to stay indoors.
Meanwhile, 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 mobile phones.
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.
Authorities 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, a campus police officer was shot and killed at Massachusetts Institute of Technology and the authorities were searching for the person responsible.