A teenager opened fire at a school in the US state of Nevada Monday, killing a teacher and critically wounding two students, police and reports said.

The shooting, which a witness said happened near a basketball court at the Sparks Middle School in Reno, also left the young gunman dead.

"The one deceased is a staff member of the school," Washoe County School District police chief Mike Mieras told reporters, adding: "The other deceased individual at this point in time appears to be a student-slash-suspect in this case."

Authorities have not released details on the shooter's identity, his motive or how he died.

Two students rushed to Renown Regional Hospital were listed in critical condition, said hospital spokeswoman Angela Rambo, cited by NBC News, after the shooting at around 1415 GMT.

Mieras said later that one of the students had undergone surgery, and the other was "doing well."

With details of what happened still emerging, a teenage witness described seeing a fellow student, wearing a school uniform, shoot a teacher in the chest.

"We were by the basketball court, and we heard a loud pop, and everybody was screaming," 13-year-old Kyle Nucum told the Reno Gazette-Journal, saying a teacher went to investigate.

"I thought it was a firecracker at first," Nucum said.

"The student was pointing a gun at the teacher, after the teacher told him to put it down... and then the student fired a shot at the teacher and the teacher fell and everybody ran away."

"We ran across the field to get somewhere safe, and while we were running we heard about four or five more shots," he added.

US Senate Majority Leader Harry Reid, who represents Nevada, sent his condolences to the school community.

"My thoughts are with teachers, parents and students at Sparks Middle School who experienced a traumatic morning," he said on his Twitter feed.

"Nevada mourns with them."

In a separate gun-related incident in the western state Monday, one man was killed and three guards shot and injured at a Las Vegas nightclub, police said.

A man paid to enter Drai's nightclub in Bally's casino on the gambling city's famed Strip in the early morning hours, but a short time later asked for his money back.

A fight broke out, during which three security guards were injured, and a patron who tried to help subdue the gunman was killed, according to Las Vegas Metropolitan Police Department spokesman John Sheahan.

The latest shootings will inevitably fuel America's perennial debate about gun control, re-ignited in traumatic fashion by last December's massacre at a school in Newtown, Connecticut, which killed 26 -- including 20 young children.

In the wake of that rampage, President Barack Obama pledged to vigorously pursue "sensible" gun control, after little was done following other recent mass shootings in the states of Colorado and Arizona.

Perhaps America's most notorious school shooting was when students Eric Harris and Dylan Klebold attacked the Columbine High School in Colorado in April 1999, killing 13 and wounding 23 before turning their guns on themselves.