Three people were killed in a shooting at the Las Vegas campus of the University of Nevada (UNLV) on Wednesday morning.
The gunman, described as a white former college professor in his 60s, was killed in a shootout with police.
The police have not identified the victims, but US media reports say that none were students.
The campus, about two miles from the world-famous Las Vegas Strip, will remain closed on Thursday and Friday.
The BBC’s US partner CBS News reported that the gunman has been identified as Anthony Polito and that he had applied for a position at the University.
Law enforcement sources told CBS News earlier that the professor previously taught in Georgia and North Carolina.
Speaking at a Wednesday press conference, Kevin McMahill, the Las Vegas Metropolitan Police Department’s sheriff, also said that they had “no idea on the motive” as of now and did not have details on his weapon.
There have been more than 630 mass shootings in the US this year. Las Vegas is also the site of the deadliest mass shooting in modern US history, where more than 50 people were killed at a music festival in 2017.
The university first tweeted at around 11:53 local time (19:53 GMT) on Wednesday that police were responding to reports of shots fired on campus.
About 20 minutes later, the university said campus police were responding to an additional report of shots near the Student Union building.
It warned students at Beam Hall, home to the university’s business school, to “evacuate to a safe area” and to “RUN-HIDE-FIGHT”, which is a common active shooter protocol in the US.
The gunman moved among the floors of Beam Hall before exiting the building, according to police.
Adam Garcia, university police chief, said the suspect was then killed in a shootout with two officers.
Sheriff McMahill said the university force’s response saved the lives of students who were gathered outside of Beam Hall playing games and eating food.
“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,” he said.
The surviving shooting victim is in stable condition at a local hospital, the sheriff said. Four other people were also taken to hospital for panic attacks and two police officers were treated for minor injuries.
One student who was on campus told a local ABC station that it seemed like police were on campus right away.
Describing the scene to the reporter he said: “You don’t know what to do. You’re calling your family, texting your friends like ‘I love you guys’ because he [the shooter] could burst through the door at any minute.”
President Joe Biden said in a statement that UNLV is the “latest college campus to be terrorized by a horrific act of gun violence” and that he and First Lady Jill Biden are “praying for the families of our fallen”.
Carolyn Goodman, mayor of Las Vegas, called it “tragic and heart-breaking news” and said she was “praying for everyone on campus”.
The Federal Bureau of Investigation (FBI) and The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are assisting local police with the investigation.
Late on Wednesday night, students were allowed back into their campus housing, with the university tweeting that there would be a “strong police presence”.
