Officials at California State University, San Bernardino said the gunfire was reported at about 6 p.m. Wednesday.
Kimberly Cheng, a reporter with Los Angeles television station KTLA, tweeted that the San Bernardino Police Department told her that there was no active shooter.
Investigators were searching the campus for one or more possible shooters.
All classes were canceled Wednesday night as police investigated.
The school about 60 miles east of downtown Los Angeles has about 20,000 students.
In a 5:59 p.m. tweet, the university announced there had been a report of shots fired near the Visual Arts Building and a parking garage. It was not immediately clear which one, but authorities were focused on the Visual Arts Building and Parking Structure West; earlier, the university had indicated that was the general area where the apparent shots had been heard.
"Don't try to leave campus", the university tweeted.
There were no reports of any injuries.
Campus police are going are escorting students from cleared buildings, there is still no estimated time for the lockdown to be lifted.
"Police are making progress in clearing buildings, but please be patient and continue to shelter in place until police clear your building".