"The campus is now open," read an email alert from the university. "Classes are in session."
The shooting occurred outside a the Ronald Tutor Center, where a party hosted by a campus student organization was being held Wednesday night, the Los Angeles Times reported.
Witnesses said more than 100 people were outside the center when an argument broke out between two men.
Capt. David Carlisle of the university's Public Safety Department said Thursday one of the men pulled a gun and started firing at his intended target. He said the victim was critically injured and taken to a local hospital for surgery.
"You hear one shot and you're like, 'Wait, what was that?'" graduate student Matthew Hamilton, who witnessed the incident, told the Times. "As soon as it registered, everyone just ran."
Three other people also were taken to area hospitals with non-life-threatening injuries, the Times said.
Police caught the suspects, one thought to be the shooter, near the scene.
The campus was on lockdown for a brief time after the shooting.