University officials confirmed nine shots were fired outside the building at around 8:40 p.m.
A shelter-in-place order was issued. The order was given an all clear at 9:45 p.m.
Cellphone video from inside the student union shows students running for safety.
ABC7 News was at the scene when a man was being pinned to the floor and carried to a police vehicle.
"I was a little bit shocked this all happened in a student building - you hear of shots taking place around the surrounding area, but you never hear about it in a university building, and we are standing by - we have to notice so much cops drive by where we were - so I'm just wondering what the school will do about security measures," said Rayaan Bhushan.
UPDATE: Video shows moments leading up to UC Berkeley suspect firing shots on campus
It's unclear what led up to the shooting. Officials only said there was an "altercation."
Students told us a campus-wide digital alert did not go out until 30 minutes after the incident.
Editorial Note: Interviewee's name was misspelled in the video. It has been corrected in the article.
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