A shooter opened fire at an elementary school in Newtown, Connecticut, on Friday, killing several people including children, the Hartford Courant newspaper reported.
The shooter was also killed, the Courant said.
Sandy Hook Elementary School teaches children from kindergarten through fourth grade - roughly ages 5 to 10.
Television images showed police and ambulances at the scene, and parents rushing toward the school. Parents were seen reuniting with their children and taking them home.
All Newtown schools were placed in lockdown after the shooting, the Newtown Public School District said.
The shooter, an adult, was dead and two handguns were recovered from the scene, NBC News reported without citing a source.
Danbury Hospital, about 11 miles west of the school, had received three patients from the scene, a hospital spokeswoman told NBC Connecticut. The mayor of Danbury, Mark Boughton, told MSNBC: "They are very serious injuries."
A girl interviewed by NBC Connecticut described hearing seven loud "booms" as she was in gym class. Other children began crying and teachers moved the students to a nearby office, she said.
"A police officer came in and told us to run outside and so we did," the unidentified girl said on camera.
One child was carried from Sandy Hook Elementary School by a police officer, and the child appeared to have been wounded, the town's weekly newspaper, the Newtown Bee, said on its website.
Connecticut State Police said its officers were at the scene with local police but provided no additional details. The emergency call to police occurred at 9:41 a.m., state police said.
An individual answering the phone at the Newtown Police Department declined to comment.
Newtown, with a population about 27,000, is in northern Fairfield County, about 45 miles southwest of Hartford and 80 miles northeast of New York City.
Sandy Hook is one of four elementary schools in the district.
The United States has experienced a number of mass shooting rampages this year, most recently in Oregon, where a gunman opened fire at a shopping mall on Tuesday, killing two people and then himself.
The deadliest attack came in July at a midnight screening of a Batman film in Colorado that killed 12 people and wounded 58.