It was no shock to family members that Landsberry - a married military veteran with two stepdaughters - would take a bullet.

"To hear that he was trying to stop that is not surprising by any means," said Chanda Landsberry, his sister-in-law. She added his life could be summed up by his love of family, his students and his country.

On his school website, Michael Landsberry posted a picture of a brown bear and told students, "I have one classroom rule and it is very simple: 'Thou Shall Not Annoy Mr. L."'

Sparks Mayor Geno Martini said Landsberry served two tours in Afghanistan with the Nevada National Guard and was well known in the school community.

"He proudly served his country and was proudly defending the students at his school," he said.

Sparks, a city of 90,000 that sprung out of the railway industry, lies just east of Reno. Students at Sparks Middle School were filing off buses and reuniting with friends after a week's holiday when the pop of gunfire shattered the morning calm.

Children fled for their lives before the first bell rang.

Law enforcement officials said the shooter opened fire with a semi-automatic handgun. It's not known where the boy got the gun.

A 13-year-old eighth grader, Kyle Nucum, told the newspaper that he heard about half a dozen shots.

Authorities did not provide a motive for the shooting.

However, 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,'" Hernandez told the paper.

The two 12-year-old wounded students were listed in stable condition. One was shot in the shoulder, and the other in the abdomen.

Parents clung to their teary-eyed children at an evacuation centre, while the community struggled to make sense of the latest episode of schoolyard violence to rock the nation less than a year after the massacre of 20 children and six adults at an elementary school in Newtown, Connecticut.

Video: Police lockdown school and evacuate children, investigation begins

Investigators were still trying to piece together the chain of events on Monday morning, 15 minutes before classes were to begin for 700 students.

"The best description is chaos," Reno Deputy Police Chief Tom Robinson said. "It's too early to say whether he was targeting people or going on an indiscriminate shooting spree."

The mayor praised the quick response from law officers, who arrived at the scene within three minutes of the initial 911 calls to find the shooter with a self-inflicted wound to the head.