Reports also said children were shot but it remains unclear whether any were killed at Sandy Hook Elementary School in Newtown.
Authorities said the gunman, who was not identified, is dead. An official with knowledge of the situation told the Associated Press that the man apparently had two guns.
Earlier reports of a second gunman are unconfirmed. The Connecticut Post reports that police are also questioning a handcuffed man in connection with the shooting. Witnesses told the newspaper he was led out of the woods by officers.
Shortly after 9:40 a.m., authorities reported that a shooter was in the main office of the school. A person in one room had "numerous gunshot wounds," police told the Hartford Courant.
A dispatcher at the Newtown Volunteer Ambulance Corps said a teacher was shot in the foot and taken to Danbury Hospital, but it was not clear if that was the only injury.
The Newtown School District has locked down schools as a preventive measure to ensure the safety of students and staff.
State police spokesman Lt. Paul Vance said they have a number of personnel on the scene to assist.
A statement on the district's website stated that afternoon kindergarten classes have been canceled.
The elementary school has close to 700 students.
Newtown is in Fairfield County, about 45 miles southwest of Hartford and 60 miles northeast of New York City.
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FoxNews.com's Cristina Corbin and The Associated Press contributed to this report.
Read more: http://www.foxnews.com/us/2012/12/14/police-respond-to-shooting-at-connecticut-elementary-school/#ixzz2F39SXwJO