A 12-year-old student armed with a handgun shot and killed a teacher and injured two classmates before taking his own life at his middle school in Nevada.
The incident happened shortly before classes began this morning.
Both of the injured students from Sparks Middle School were rushed to Renown Regional Medical Center in nearby Reno.
One school child underwent emergency surgery, said Tom Miller, acting Sparks police chief.
The Reno Gazette-Journal newspaper identified the slain school staff member as 45-year-old maths teacher Michael Landsberry.
A seventh-grade student identified as Andrew told local KOLO-TV that: "a kid started getting mad and he pulled out a gun and shoots my friend, one of my friends at least," "And then he walked up to a teacher and says back up, the teacher started backing up and he pulled the trigger."
He said: "The teacher was just lying there and he was limp, he didn't know what to do, he was just in a lot of pain."
"And me and five other friends went to him and said come on we've got to get him to safety. We picked him up, carried him a little bit far and we left him because our vice principal came along and said go, go, go get to safety, get to safety. So we left the teacher there and we went to safety," Andrew said.
Family members of Mr Landsberry described him as a hero who tried to persuade the young gunman to drop his weapon.
In Sparks, a 13-year-old eighth grader, Kyle Nucum, told the Gazette-Journal that he heard about half a dozen shots. Student Michelle Hernandez said she had seen the suspect before the shooting began.
"I heard him saying, 'Why you people making fun of me, why you laughing at me.'" Michelle Hernandez told the paper.
150 to 200 police officers descended on the school following the shooting and searched the grounds with bomb dogs,Reno deputy police chief Tom Robinson said.
Agents from the FBI and US Department of Homeland Security were assisting in the investigation, he said.
Mr Robinson said it was too early to tell if the boy, who was not immediately identified by authorities, was targeting anyone in the shooting rampage.
Authorities also declined to immediately speculate on his motives.
Classes and after school activities were cancelled at Sparks Middle School for the rest of the week and counsellors would be on hand to work with students and staff members who were traumatised by the shooting, the school district said.