Multiple people, including children, have been killed in a shooting at Sandy Hook Elementary School.

The number of dead is unclear, but there are at least 20 shooting victims. Many of the shootings took place in a kindergarten classroom, sources said.

One entire classrom is unaccounted for outside the school, sources said.

A person believed to be a shooter is dead. Earlier reports of a second shooter are unconfirmed.

CBS News is reporting that 27 people are dead.