The search was centered on three buildings along Nutwood Avenue on the southeast edge of the campus, said Chris Bugbee, the school's director of public relations. Students were alerted via text message Wednesday evening and told to shelter in place.
Some occupants of Mihaylo Hall at the university's College of Business were evacuated.
"We saw all these cops coming through with I think they were like AKs or something. They were pretty big guns. And they eventually told us we had to leave the campus," student Nate Chu told KABC-TV.
At least one person fired a handgun while attempting to rob the jewelry store in Moreno Valley just after 3 p.m., according to Riverside County Sheriff's Cpl. Angel Ramos. One person was shot, and the victim's condition was unknown.
Five suspects fled the robbery in a gray Lexus and were stopped by police in Fullerton when the Lexus rear-ended a vehicle near the school. Two people were detained soon after the crash. Three others ran off.
"They ran right at me, I decided to get out of their way, I did not know if they were armed or not," said student Shaun Kintaudi, who was on his way to take a test. "I decided it was best to run away from them and let the cops do their job."
The suspects were considered armed and dangerous, said Fullerton police spokesman Jeff Stuart.
All students were safe, school officials said. Some posted photos to Twitter and Facebook of their locked-down classrooms and dorm rooms with doors barricaded as they waited inside, watching the news on their laptops.
"We've made a makeshift bathroom out of trash cans, and whatever happens here stays here, that's the rule," Robert Pachorek, a student stuck in a classroom in Langsdorf Hall, told KABC-TV.
All evening classes and activities were canceled Wednesday. The campus is in its final week of classes before final exams.
One of the suspects who fled after the crash near campus carjacked a silver sedan and drove onto westbound state Route 91, speeding erratically through rush hour traffic until it exited onto surface streets in Los Angeles County.
The suspect ran from the car and surrendered to dozens of officers on a baseball diamond at a recreation center in Watts, where LA Police Chief Charlie Beck was giving away toys to hundreds of young children.
"He picked the wrong rec center to run into today," said LAPD Cmdr. Andy Smith.