A person rides a scooter by crime scene tape in the aftermath of a shooting at the University of Nevada, Las Vegas. AP

Three people were killed and another seriously injured by a gunman who was shot dead by police at a US university on Wednesday.

The incident at the University of Nevada, Las Vegas, a short distance from the gambling hub's tourist-packed Strip, was the latest in the United States, where gun violence is a part of the fabric of daily life.

"Three of the victims are confirmed deceased," Las Vegas Sheriff Kevin McMahill told a press conference.

He said a fourth victim had been critically injured by the shooting but that condition later upgraded to stable.

The identity of the shooter was not immediately released, but CNN and the Los Angeles Times, quoting law enforcement sources, said he was a 67-year-old career college professor with links to schools in Georgia and North Carolina. But it was not clear what affiliation he had with the Nevada university where the shooting took place.

Students listen as gun violence survivors speak during a national vigil in Washington, DC. AFP

US 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 at 11:45 am (1945 GMT), McMahill told a press conference.

Two officers "immediately engaged the suspect in a shootout" and the suspect "was struck and is deceased at this time," said university police chief Adam Garcia.

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."

Police did not provide any further information on the identities of the victims or gunman, and are in the process of notifying next-of-kin.

Agence France-Presse