A shooting in a Connecticut primary school has left 27 people dead, including 18 children, many of them as young as five years old.

According to reports, a masked gunman opened fire on a kindergarten classroom at Sandy Hook Elementary School in the town of Newtown.

A student at the school told NBC Connecticut that she heard seven loud "booms" while she was in gym class.

"A police officer came in and told us to run outside and so we did," she said.

A news conference was set to be held at 6pm BST but has been delayed.

Connecticut School Massacre: 18 Children among 27 Dead in Sandy Hook Shooting