Oakland police officers enter a Oikos University building after a school shooting in Oakland, Calif., Monday. (AP-Yonhap News)

Seven people were killed and three injured Monday when a gunman opened fire at a private California religious college near San Francisco, officials said.

The suspected gunman -- who was later detained -- stood up in class and shot one person at point blank range in the chest, before spraying the room with bullets, according to an injured witness cited by the San Francisco Chronicle.

"There are seven (families) now that are having to deal with this horrendous act," Oakland City Council president Larry Reid told CNN, after the shooting at Oikos University in East Oakland.

The motive for the shootings was unclear, said the city official, who had been briefed by Oakland's chief of police.

"Our police department right now is doing their work and trying to understand what in fact was his motive to come and take the lives of seven individuals, and then also to leave three individuals wounded," Reid said.

"That information will come out during the legal process that he now finds himself in," he said.

Initially police warned that a suspect, described as Korean and in his 40s, was at large, but a short time later, the Oakland Police Department said on Twitter that they had a "possible suspect in custody."

"No imminent public safety threat appears to exist in immediate area," it added.

The suspect was arrested some eight kilometers away outside a Safeway supermarket in Alameda, according to the Oakland Tribune, which cited a witness as saying the suspect was calm as he was taken into custody.

Lisa Resler, 41, said she was leaving the Alameda store with her daughter when she saw a young Asian man wearing a hat being confronted by store security. She described him as looking "very sedated" as he was handcuffed.

Within minutes of the mid-morning shooting, SWAT teams took position around the building, some smashing glass with sledgehammers and rushing inside as officers helped students evacuate the campus, the Chronicle reported.

Angie Johnson, 52, said she saw a young woman leaving the building with blood coming from her arm and crying, "I've been shot, I've been shot."

The woman said the shooter was a man in her nursing class who rose up and shot one person at point blank range in the chest before he started spraying the room with bullets, Johnson said, cited by the Chronicle.

"She said he looked crazy all the time," Johnson said the victim told her.

"But they never knew how far he would go."

The victim "had a hole in her right arm the size of a silver dollar with blood coming down," she added.

Five ambulances were dispatched to a "multi-patient medical scene," the Oakland Fire Department said on its Twitter feed, while police described the suspect as "male, Asian, heavy build, khaki clothing."

The school says on its website that it strives to "provide highest standard education with Christian value and inspiration."

"Oikos University has a very specific goal and mission to offer education programs in the area of religious studies, music, and vocational nursing," it said.

"We motivate, educate and equip students in such a way that they will be able to live an enriched life by fulfilling their goals in life and serve the community with their learned professions and skills," it added.

Police were due to hold a press conference at 6:00 p.m. Monday to give more details about the shooting. (AFP)