A gunman has shot dead a police officer at the Massachusetts Institute of Technology (MIT) in Cambridge near Boston, officials say.
Cambridge police say the officer was responding to a report of a disturbance in the area when he was shot and suffered “multiple wounds”.
He was taken to hospital where he was pronounced dead.
Police say they are still looking for the gunman and the campus is on lockdown.
A statement on the university’s website says a building there is surrounded by the emergency services.
The statement says the situation is considered “extremely dangerous”.
TV footage showed police swarming around the university’s Stata Center.
The university is advising students to stay clear of the area until further notice.
A statement from the Middlesex district attorney’s office said there are no other victims and no arrests have been made