Oikos University was surrounded by armed police after the shootings yesterday, which left several other people in hospital.
Oakland Police said a suspect was in custody and there was no immediate threat to anyone in the area. However, the college continued to be the centre of a major police operation for some time after the shootings.
The incident happened at about 10:50am local time. Reports suggested the former student went to the college carrying a gun.
Local television news pictures showed police evacuating the campus and loading students into a police vehicle as armed officers took up positions around the school. Police were seen covering bodies that lay on the grass around the university campus.
Oakland City Council president Larry Reid said he was told by police at least six people had been killed and three injured.
At a press conference, Oakland Police confirmed seven people had died.
Earlier, police spokeswoman Johnna Watson said: “A gunman came into the college and fired multiple shots. We do have fatalities. I cannot confirm the number of fatalities.
“We additionally have victims who have gunshot wounds.”
One witness, Brian Snow, told local television news: “One of the people who was inside the building, she was saying there is a crazy guy inside.
“She did say someone got shot in the chest right next to her before she got taken off in an ambulance.”
Angie Johnson, who was near the school when the shootings started, told the San Francisco Chronicle she helped a woman with a gunshot wound in her arm. She “had a hole in her right arm the size of a silver dollar with blood coming down”, Ms Johnson said.
Early reports described the suspect as a Korean man who was in his 40s and had a heavy build. He was said to have been wearing khaki clothing. Early reports suggested he was arrested at a shopping centre some distance from the university
Ms Watson said police were still working to secure the building and ensure the safety of students.
She went on: “We have cordoned off the area and set up a perimeter for public safety.
“In that area right now, we have medical personnel; we have our officers as well as our Swat teams. They are still evacuating any possible injured or students from this college.
“It is still a very active and fluid situation.”
Describing the scene as “a very tense situation” she added that officers were taking witness statements from those present who had escaped.
Officials at the Highland Memorial Hospital in Oakland, which is near the campus, said medical staff were treating four shooting victims.
Oikos University is a private religious institution and specialises in theology, music, nursing and Asian medicine. It particularly attracts students from the Korean Catholic community.
The university describes itself on its website as having been started to provide the “highest standard education with Christian value and inspiration”.
Pastor Jong Kim, who founded the school about ten years ago, told the Oakland Tribune the alleged shooter was a nursing student who was no longer enrolled. He did not know if the he had been expelled or had dropped out.
Mr Kim said he heard about 30 rapid-fire gunshots in the building. “I stayed in my office,” he added.