Connecticut School Shooting: Multiple Deaths, including Children and Gunman, Reported after Shooting at Sandy Hook Elementary School in Newtown

An unidentified person who walked into an elementary school early Friday morning in Newtown, Conn., and opened fire, killing multiple people, including children, authorities reported before 12 p.m. Friday.

State Police officials told ABC News the gunman is dead after an early morning day at Sandy Hook Elementary school in Newtown, just 12 miles east of Danbury, turned chaotic when gunfire erupted in a school full of small children.

The Hartford Courant reported at 12:06 p.m. Friday that sources are saying that multiple people, including children, were killed during the shooting, though the number of victims is not clear at this time. According to NBC News, as of 12:40 p.m., report at least 20 have been killed.

The first 911 calls came at 9:41 a.m., reporting that multiple students were trapped in a classroom, possibly with a gunman. Police sent emergency units from western Connecticut to the school.

Danbury Mayor Mark Boughton told USA Today that several victims had been taken to local hospitals, although details were not readily available.

While some students have been reunited with their parents on the outskirts of the school, one group of students remains unaccounted for, according to a source with a child in the school.

Eight-year-old Alexis Wasik, a third-grader at the school, told the Courant that police were checking everybody inside the school before they were escorted to the firehouse.

"We had to walk with a partner," she said.

A spokesman for Gov. Dannel P. Malloy, told the Courant that the governor is monitoring the situation and is in "constant contact" with state police, who are coordinating with federal and local officials. 

This marks the second mass shooting this week, after a 22-year-old gunman on Tuesday opened fire with a semiautomatic weapon at a mall in Clackamas County, Oregon, killing two people and wounding a third teenage victim before killing himself.

An announcement on the school's web site says that kindergarten classes have been cancelled for Friday, and there will be no mid-day bus runs.

President Barack Obama has been notified and briefed of the shooting.