At least 27 people, including 14 children, were killed Friday in a shooting at an elementary school in Connecticut, CBS News reported.

The shooting incident took place at Sandy Hook Elementary School in Newtown, Connecticut, about 12 miles east of Danbury.

ABC News reported that the massacre involved two gunmen, prompting the town of Newtown to lock down all of its schools and draw SWAT teams to the school.

State Police confirmed that one shooter is dead. A second gunman is apparently at large. Car-to-car searches are underway.

It is the worst shooting in a U.S. elementary school in recent memory, noted the report.

While some students have been reunited with their parents on the school’s perimeter, one group of students remains unaccounted for, a source with a child in the school told ABC News.

The school is kindergarten through fourth grade and has about 450 students.

Three patients have been taken to Danbury Hospital, which is also on lockdown, according to the hospital’s Facebook page.