Police say three people have been killed in a shooting at the Las Vegas campus of the University of Nevada (UNLV) on Wednesday morning.
Officers struck and killed the suspect, who remains unnamed, in a shootout.
One other victim remains in a critical condition at a local hospital, police said in a statement.
Law enforcement sources speaking to US broadcaster CBS described the gunman as a white former college professor in his sixties.
They added he had previously taught in Georgia and North Carolina.
UNLV and all other southern Nevada System of Higher Education institutions across the state were to remain closed for the rest of Wednesday.
The university first tweeted at around 11:53 local time (19:53 GMT) 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 to "evacuate to a safe area" and to "RUN-HIDE-FIGHT", which is a common active shooter protocol in the US.
Adam Garcia, university police chief, said two campus officers engaged the suspect in a shootout before being was struck and killed.
Kevin McMahill, Las Vegas Metropolitan Police Department sheriff, said earlier at a press conference that they had "no idea on the motive" as of now.
One additional victim is in stable condition at a local hospital, the sheriff said at a Wednesday evening press conference. 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."
A ground stop was issued earlier at Las Vegas' Harry Reid International Airport - which is near the school - with authorities citing security reasons.
The airport is urging travellers to check their flight status and notes roadways around the airport are closed due to police activity.
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".
Shortly before 13:00 local time, the university said police were "evacuating buildings one at a time".
Nevada's Governor Joe Lombardo said his office was in "constant communication" with Las Vegas police, the university and emergency responders.
The Federal Bureau of Investigation (FBI) and The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are assisting local police with the investigation.
The Clark County Fire Department has established a family reunification centre at the Las Vegas Convention Center.
The UNLV campus will also be closed on Thursday and Friday.
