A teacher was shot dead and two students were wounded when a student opened fire at a middle school in the northern Nevada city of Sparks on Monday before taking his own life, law enforcement officials said.

Both of the wounded students from Sparks Middle School were listed in critical condition at Renown Regional Medical Center in nearby Reno, where one of them had undergone emergency surgery, said Tom Miller, acting Sparks police chief.

"A kid started getting mad and he pulled out a gun and shoots my friend, one of my friends at least," a seventh-grade student identified as Andrew told local KOLO-TV. "And then he walked up to a teacher and says back up, the teacher started backing up and he pulled the trigger."

"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," Andrew told KOLO.

"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," he said.

The incident marked the latest in a string of shooting rampages across the United States in recent years, some of them at schools, that have reignited a national debate over gun control.

In Connecticut last December, 20 students and six adults were shot to death by a gunman at a school in Newtown before the attacker took his own life in what is considered one of the worst school shootings in US history.

"It's a tragic day for the city of Sparks," Mayor Geno Martini told a late-morning news conference. "I just want to reiterate again that the city itself is very safe and this is just an isolated incident. But it's very, very tragic and I'm saddened to be here to have to tell you this."

Law enforcement officials said the student gunman opened fire at 7:16 a.m. local time, about 15 minutes before classes were scheduled to begin at the school, which serves seventh and eighth grade students.

"Students are arriving, buses are arriving ... Kids are congregating out back to play sports or waiting for the first bell to ring. The bell rings at 7:30," said Mike Mieras, Washoe County School District police chief.

They said it was too early to tell if the boy, who was not immediately identified by authorities, was targeting anyone in the shooting rampage. They declined to speculate on his motives pending further investigation.

Classes at the middle school and a neighboring elementary school were canceled and authorities said counselors would be on hand to work with students and staff members who were traumatized by the shooting.

"My administration is receiving regular updates and the Nevada Highway Patrol is assisting at the scene," Nevada Governor Brian Sandoval said in a statement.