Twenty-seven people have been killed, including 20 children, by a gunman at Sandy Hook Elementary School in Newton, Connecticut.
The identities of the victims have not as yet been revealed.
Police also confirmed the gunman was also "deceased in the school". They have not confirmed his identify but have said that a "tentative identification" has been made.
ITV News' Robert Moore reports.
Lieutenant Paul Vance from Connecticut State Police confirmed the fatalities at a news conference.
There were 18 children who were pronounced dead at the school, there were two that were transferred to an area hospital and pronounced dead there, and there were six adults pronounced dead at the school.
He also said that another adult victim was found dead at a second location in Connecticut.
President Obama described the shooting as a "heinous crime".
Visibly emotional, the president wiped away a tear as he gave a statement at the White House.
He said: "Our hearts are broken for the parents...There are no words that will ease their pain".
President Obama also directed US embassies to fly flags at half-mast in tribute to the victims.
There have been unconfirmed reports that the gunman's mother was among the school shooting victims.
The Associated Press reports that law officials have said the brother of the gunman is being held by officers for questioning.
The families of those affected by the Sandy Hook Elementary School shooting have assembled in a building near the school waiting to hear news of their children and loved ones.
Earlier, young children described their experience of being led out of the school during the shooting.
One young student said: "We were running really quick, and then we got to the firehouse, and then we were all happy we were still alive."
As worried parents heard news of the shooting, many rushed to the school to pick up their children.
Police swat teams responded to the active scene and thoroughly searched the area around the school.