URGENT: Twenty-seven people, including 20 children, were killed Friday when a gunman clad in black military gear opened fire inside his mother's kindergarten class at a Connecticut elementary school.
The shooter, who sources identified as Adam Lanza, 20, gunned down his mother and her entire class at Sandy Hook Elementary School in Newtown, Conn., according to sources. Lanza was found dead inside the school, according to officials. Eighteen of the children and six more adults were dead at the school and two more children died later, according to Connecticut State Police Lt. Paul Vance.
Vance would not confirm the shooter's name, and earlier in the day there were conflicting reports over the gunman's identity. Law enforcement sources told FoxNews.com the shooter was Adam Lanza. His brother, Ryan Lanza, 24, was being questioned in Hoboken, N.J., but it was not sure if he faced charges.
"It is not a simplistic scene," Vance told reporters.
An official with knowledge of the situation said the shooter was armed with a .223-caliber rifle. Four weapons in total were recovered from the scene. The motive is not yet known.
Vance said during an afternoon news conference that police arrived at the scene "within minutes" of a 911 call placed shortly after 9:30 a.m.
"Every door, every crack, every crevice of that school" was checked, Vance said. “The entire school was searched.” He said the shooting occurred inside two rooms in "one section of the school."
Vance did not give details about the number of victims other than to say they included students and staff, pending notification of the families. He said more information would be released, possibly later Friday.
Vance also said that a "deceased adult" was found at a "secondary crime scene," though he declined to elaborate.
A federal law enforcement official told Fox News that Lanza's mother, Nancy, was killed at her home in Connecticut. The vehicle the suspect used in the shooting was registered to his mother.
A dispatcher at the Newtown Volunteer Ambulance Corps said earlier a teacher was shot in the foot and taken to Danbury Hospital. Local news outlets also reported that the principal was among those shot.
Robert Licata said his 6-year-old son was in class when the gunman burst in and shot the teacher.
"That's when my son grabbed a bunch of his friends and ran out the door," he said. "He was very brave. He waited for his friends."
He said the shooter didn't utter a word.
Stephen Delgiadice said his 8-year-old daughter was in the school and heard two big bangs. Teachers told her to get in a corner, he said.
"It's alarming, especially in Newtown, Connecticut, which we always thought was the safest place in America," he said. His daughter was fine.
Mergim Bajraliu, 17, heard the gunshots echo from his home and ran to check on his 9-year-old sister at the school. He said his sister, who was fine, heard a scream come over the intercom at one point. He said teachers were shaking and crying as they came out of the building.
"Everyone was just traumatized," he said.
President Obama was notified of the shooting around 10:30 am ET, White House officials said.
"Our hearts are broken today," Obama said in a brief address to the nation on Friday. "We've endured too many of these tragedies in these past few years, and each time I receive the news I react not as a president, but as a parent."
"Most victims were children, between five and 10 years old...They had their entire lives ahead of them, birthdays, graduations weddings, kids of their own," he said, pausing before wiping tears from his eyes.
Sandy Hook 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.
FoxNews.com's Cristina Corbin, Jana Winter, Perry Chiaramonte, Mike Levine and The Associated Press contributed to this report.