Gunshots have reportedly been heard near a building at the Massachusetts Institute of Technology (MIT) in Boston.
The area is has been surrounded by "responding agencies", .
A statement on the website says the area has been cordoned off and warned students to stay away.
There appears to be little detail on the identity of the shooter.
A local television station says an officer has been shot, quoting the MIT campus police chief.
It is believed the officers has been rushed to Massachusetts General Hospital.
The incident has happened late at night and the numbers of students on campus is expected to be lower.
It comes after two bombs at the city's marathon killed three people and injured 180 on Monday.
Responding agencies continue to investigate active shooter incident at building 32 (Stata). Please stay indoors and away from the area.
— MIT (@MITnews)
More to follow.