[Updated 5:37 a.m. ET]
Boston Police, via its official Twitter account, says businesses near 480 Arsenal Street in Watertown, Massachusetts, are closed until further notice. Employees are also instructed to stay home.
[Updated 5:20 a.m. ET]
MIT cancels Friday's classes, according to a letter from Israel Ruiz, the school's executive vice president and treasurer, and school Chancellor Eric Grimson.
"MIT suffered a tragedy last night: an MIT Police officer was shot and killed on our campus in the line of duty," says the letter, addressed to the MIT community. "While the circumstances around the officer's death remain the subject of an active investigation, what is certain is that the officer gave his life to defend the peace of our campus. His sacrifice will never be forgotten by the Institute. We are thinking now of his family, and our hearts are heavy. In consultation with faculty chair Sam Allen, we have decided to cancel classes today (Friday). All employees are encouraged to use their best judgment about whether they are prepared to come in to work today: any absence today will be considered excused."
[Updated 5:03 a.m. ET]
Police in Watertown sending robocalls to residents instructing them to stay indoors, reports CNN's Drew Griffin.
[Updated 4:45 a.m. ET]
One of the suspects believed to have planted bombs at the Boston Marathon is dead after a shootout with police, a police spokesman said.
[Updated 4:21 a.m. ET]
The suspect on the loose in Watertown, Massachusetts, matches the description of Suspect 2 -- a man pictured wearing a white cap - wanted in connection with the bombings at the Boston Marathon on Monday, police said early Friday.
[Updated 3:54 a.m. ET]
Massachusetts State Police, via Twitter: "Police will be going door by door, street by street, in and around Watertown. Police will be clearly identified. It is a fluid situation."
[Updated at 3:48 a.m. ET]
Massachusetts State Police, on its official Twitter feed, warns Watertown residents to stay in their homes and to not answer the door "unless it is an identified police officer." "If any concerns about someone at door, call 911 immediately. Repeat--Do not answer door, stay away from windows, keep doors locked," the state police says in another tweet.
[Updated 2:40 a.m. ET]
Massachusetts State Police spokesperson Dave Procopio said that they believe multiple possible explosive devices were used against police tonight during this incident at Watertown. It was unclear if the incident, which followed a police chase of a stolen vehicle, was related to the shooting on the MIT campus or any other incident in the Boston area.
[Updated 2:31 a.m. ET]
FBI spokesman Martin Feely tells CNN's Susan Candiotti: "We are engaged with our partners trying to determine if there is a connection." CNN's Drew Griffin, who is on the scene in Watertown, Massachusetts, said FBI agents are on the scene.
[Updated 2:21 a.m. ET]
MIT releases statement on shooting death of campus police officer: "MIT is heartbroken by the news that an MIT Police officer was shot and killed in the line of duty on Thursday night on campus, near Building 32 (the Stata Center). Our thoughts are now with the family." http://bit.ly/15lcg2r
[Updated 2:19 a.m. ET]
Boston Police Department's official Twitter feed says "there is an active incident ongoing in Watertown. Residents in that area are advised to remain in their homes. More details when available."
[Updated 2:07 a.m. ET]
CNN's Gabe Ramirez on the scene in Watertown, Massachusetts, says that authorities are ordering people in the area to shut off their cell phones.