A student at a Nevada school opened fire on campus just before the starting bell Monday, wounding two boys and killing a math teacher who was trying to protect children from their gun-wielding classmate.

Teacher Michael Landsberry was being hailed for his actions outside Sparks Middle School, where 20 to 30 horrified students witnessed the shooting.

“In my estimation, he is a hero. ... We do know he was trying to intervene,” Reno Deputy Police Chief Tom Robinson said.

The unidentified shooter was killed along with Landsberry, a 45-year-old military veteran who leaves behind a wife and two stepdaughters. The motive for the shooting is still unknown. One of the wounded students is out of surgery and the other is doing well, police said.

It's unclear whether the student committed suicide, but authorities say no shots were fired by law enforcement. Police said between 150 and 200 officers, including some from as far as 96 kilometers away, responded to the shooting.

The violence erupted nearly a year after a gunman shocked America by opening fire in Sandy Hook Elementary School in Newtown, Connecticut, leaving 26 dead. The Dec. 14 shooting ignited debate over how best to protect the nation's schools and whether armed teachers should be part of that equation.

Students from the middle school and neighboring elementary school were evacuated to the nearby high school, and classes were canceled. The middle school will remain closed for the week.

“As you can imagine, the best description is chaos,” Robinson said. “It's too early to say whether he was targeting people or going on an indiscriminate shooting spree.”

The shooting happened on the school's campus and ended outside the school building itself, according to police.

About 700 students in 7th and 8th grades are enrolled at the school, located in a working class neighborhood.

In a statement on the website of Sandy Hook Promise, a gun control advocacy group, Nicole Hockley, whose son Dylan was killed in the shooting said, “It's moments like this that demand that we unite as parents to find commonsense solutions that keep our children _ all children _ safe, and prevent these tragedies from happening again and again.”

Sparks, a city of roughly 90,000 that sprung out of the railway industry, lies just east of Reno. (AP)