A boy opened fire with a semi-automatic handgun at his Nevada school, killing a maths teacher who was trying to protect pupils and wounding two 12-year-old classmates, before turning the weapon on himself.
The boy killed himself after a rampage witnessed by 20 to 30 terrified children who had just returned to school from a week-long autumn break, police said. Authorities did not give a motive for the shooting, and it was not known where the boy obtained the gun.
Murdered teacher Michael Landsberry was hailed a hero for his actions outside Sparks Middle School during yesterday's shooting.
"In my estimation, he is a hero. ... We do know he was trying to intervene," Reno deputy police chief Tom Robinson said.
Both wounded boys were said to be in a stable condition. One was shot in the shoulder, and the other in the abdomen.
The violence erupted nearly a year after a gunman shocked the nation by opening fire at Sandy Hook Elementary School in Newtown, Connecticut, leaving 26 dead. The December 14 shooting ignited debate over how best to protect America's schools and whether armed teachers should be part of that equation.
Mr Landsberry, 45, was a military veteran and leaves a wife and two stepdaughters. Sparks mayor Geno Martini said Mr Landsberry served two tours in Afghanistan with the Nevada National Guard.
On his school website, Mr Landsberry posted a picture of a brown bear and took on a tough-love tone, telling students: "I have one classroom rule and it is very simple: 'Thou Shall Not Annoy Mr. L.'"
"The kids loved him," his sister-in-law Chanda Landsberry said. "To hear that he was trying to stop that (the shooting rampage) is not surprising by any means."
Police said 150 to 200 officers responded to the shooting, including some from as far as 60 miles away. Pupils from the middle school, most of them 12 and 13 years old, and a neighbouring primary school were evacuated to the nearby high school, and classes were cancelled. The middle school will remain closed all week.
"As you can imagine, the best description is chaos," Mr Robinson said. "It's too early to say whether he was targeting people or going on an indiscriminate shooting spree."
At the evacuation centre, parents comforted their children.
"We came flying down here to get our kids," said Mike Fiorica, whose nephew attends the school. "You can imagine how parents are feeling. You don't know if your kid's OK."
The shooting happened on the school's campus just before the morning bell rang and ended outside the school building, according to police.
"I was deeply saddened to learn of the horrific shooting at Sparks Middle School this morning," Nevada governor Brian Sandoval said, extending his thoughts and prayers to those affected.
About 700 children in 7th and 8th grades are enrolled at the school, in a working class neighbourhood.
"It's not supposed to happen here," Ms Landsberry said. "We're just Sparks - little Sparks, Nevada. It's unreal."
A statement from Nicole Hockley, whose son Dylan was killed in the Connecticut shooting, appeared on the website of gun control advocacy group Sandy Hook Promise.
"It's moments like this that demand that we unite as parents to find common sense solutions that keep our children - all children - safe, and prevent these tragedies from happening again and again," she said.
The Washoe County School District held a session in the spring following of the Newtown tragedy to educate parents on its safety measures. The district has its own 38-officer police department, but no officers were on campus at the time of the shooting.
Sparks, a city of about 90,000 that sprung out of the railway industry, is just east of Reno.