The United States is in shock after a man murdered his mother at home before gunning down 20 children and six adults in a Connecticut school.
The heavily armed gunman, named as 20-year-old Adam Lanza, shot the children - aged between five and 10 years old - at Sandy Hook Elementary School.
Dawn Hochsprung, the head teacher at the school in Newtown, was among those killed in the shooting, which began at around 9:30am - just after school day started.
After storming through several classrooms, Lanza, who was wearing a bullet-proof vest and carrying two handguns, turned one of the guns he was carrying on himself.
An emotional US President Barack Obama wiped tears from his eyes as he told a stunned country : "Our hearts are broken today."
Mr Obama hinted at possible gun law reform , declaring that the latest atrocity signals that the country should come together to take meaningful action, "regardless of the politics".
The President also used his weekly address to express his sadness in the wake of the shooting.
"We grieve for the families of those we lost. And we keep in our prayers the parents of those who survived. Because as blessed as they are to have their children home, they know that their child's innocence has been torn away far too early," Mr Obama said.
Children told their parents they had heard bangs and, at one point, a scream over the intercom. Teachers ordered them to hide in closets or corners.
"I was going back to my classroom and I heard like a person kicking on the door and I turned around I smelled smoke," an eight-year-old boy told NBC.
Reports said Lanza killed his mother, Nancy Lanza, and then drove to the school in her car.
Some reports said Lanza's mother was a substitute teacher at the school. But her name did not appear on a staff list.
At least three guns were found - a Glock and a Sig Sauer, both pistols, inside the school, and a high-powered rifle in the back of the car, authorities said.
A law enforcement official speaking on condition of anonymity said some of the guns used in the attack may have belonged to Lanza's mother, who had legally purchased five weapons.
The attack, just two weeks before Christmas, was America's second-deadliest school shooting, exceeded only by the Virginia Tech university massacre in 2007 that left 32 dead.
Authorities offered little clue as to the motive for the shootings in the picturesque small town northeast of New York City.
The gunman was believed to suffer from a personality disorder and lived with his mother in an affluent part of Newtown, a picturesque community of 27,000 people.
State police Lt Paul Vance said just one person suffered an injury and survived, indicating that the gunman was unusually accurate or methodical in his fire.
Lanza's older brother Ryan, 24, of Hoboken, New Jersey, has been questioned by police but a law enforcement official said he was not believed to have had any role in the shooting and was "extremely cooperative".
Ryan Lanza told law enforcement he had not been in touch with his brother since about 2010.
Hours after the shooting, hundreds of people gathered for a vigil, the crowd filling the church to capacity and spilling outside its doors.
Some lit candles while others joined hands to sing Christmas songs.
"Evil visited this community today," State Governor Dan Malloy said earlier.
David Connors, whose triplets were at the school during the shooting but were unharmed, said he was still horrified.
"It's hard. I've never imagined a thing like that could happen here."
Police said they expected to be able to make public the identities of the victims later on Saturday.
Prime Minister David Cameron said: "It is heartbreaking to think of those who have had their children robbed from them."
The Queen sent a message to Mr Obama in which she said she was "deeply shocked and saddened".
Pope Benedict XVI sent a letter of condolence to the community, which was read aloud at a vigil in Newtown on Friday evening.
UN chief Ban Ki-moon wrote to Connecticut Governor Dan Malloy to give his "deepest condolences at the shocking murders," a statement said.
"The targeting of children is heinous and unthinkable," he added in condemning the "horrendous" crime.