As many as 27 people have been killed, including many children, in a shooting attack at a primary school in the US state of Connecticut, US media say. At least 18 children are among the dead at Sandy Hook Elementary School in Newtown, the Associated Press reported.
Earlier, the gunman was reported to have been killed and at least three people were taken to hospital.
A news conference is imminent and the state Governor Dannell Malloy is on his way.
Police arrived at the school soon after 09:40 local time (14:40 GMT), answering reports that a gunman was in the school's main office and one person had "numerous gunshot wounds".
Scores of officers at the scene carried out a full search of the site.
Schools across the district were immediately on lock-down as a preventive measure, officials said.
With the death toll rising, it emerged that one entire classroom of students may remain unaccounted for, local sources reported.
Meanwhile, the three people who have been taken to hospital are in "very serious condition", Danbury Mayor Mark Boughton told CNN.
One witness speaking to CNN said that shots were heard coming from the hall. There "must have been 100 rounds" fired, she told the channel.
Local media have reported that firefighters instructed children to close their eyes and run past the school's office as they exited the building.
Other sources suggest that some of the shots were fired in a school classroom.
According to CNN, the shooter's body was in one of the school's classrooms.
There were unconfirmed reports of two shooters, according to a report in the local Hartford Courant newspaper.