A gunman killed 27 people, including 18 young children, at a US school, an official said, in one of the worst school shootings in the country's history.
State police in Connecticut, in their first hurried briefing, said only students and staff at Sandy Hook Elementary School were killed.
They said the gunman was dead inside the school, and the scene was secure. Children, some of them crying, had been rushed from the building.
The White House said President Barack Obama had been notified and that he had "enormous sympathy for families that are affected".
The attack was the latest of several mass shootings in the US this year, and approached the deadly scale of the Virginia Tech university massacre in 2007 in which 32 people were killed.
The victims of today's attack were young children. Photos from the scene showed frightened pupils being escorted by adults through a car park in a line, hands on each other's shoulders.
Children told their parents they had heard bangs and, at one point, a scream over the intercom. Anguished parents came running when they heard the news.
The shooting shocked the small, tranquil community in one of the wealthiest counties in the US, about 60 miles north-east of New York City.
A law enforcement official in Washington said the attacker was a 20-year-old man with links to the school and that one of the guns was a .223-caliber rifle.
The official also said that New Jersey state police were searching a location in that state in connection with the shootings.