The gunman who killed three people and injured another at the University of Nevada, Las Vegas was an academic who had applied for a professorship but was not hired, US media reported Thursday.

The incident at UNLV, a short distance from the gambling hub's tourist-packed Strip, marked the latest shooting in a country plagued by gun violence, and comes six years after Las Vegas suffered one of the worst mass shootings in US history.

Las Vegas Sheriff Kevin McMahill on Wednesday said there were three confirmed deceased victims and that the attacker was shot dead by police.

A fourth victim had been critically injured in the shooting but their condition later was upgraded to stable.

Early Thursday US media reported the shooter was a 67-year-old career academic, with links to schools in Georgia and North Carolina, who had applied for a professorship at UNLV but was not hired.

ABC News, citing multiple law enforcement sources, identified the suspect as Anthony Polito and said the victims were faculty or staff, and not students.

President Joe Biden in a statement decried the latest "horrific act of gun violence" to terrorize a college campus.

Police responded within minutes to reports of an active shooter, and engaged in a firefight that neutralized the gunman.

The incident began as an outdoor gathering of students was taking place.

"Students were playing games and eating food, there were tables set up for them to build Legos," said McMahill.

"If it hadn't been for the heroic actions of one of those police officers who responded, there could have been countless additional lives taken."

The killings shook a city that in 2017 was the scene of one of America's deadliest-ever shootings, when a gunman opened fire on a crowded music festival, killing 60 people.