A gunman opened fire at a private Christian college in California on Monday, killing at least seven people and wounding three others after telling former classmates to "get in line ... I'm going to kill you all."

A suspect in what was the deadliest US school shooting in five years was later arrested at a shopping mall several miles away from the scene of the shooting at Oakland's Oikos University, which appears to cater largely to the area's Korean community.

The school's founder, Pastor Jong Kim, told the Oakland Tribune newspaper that the gunman had been a nursing student there, but was no longer enrolled.

Authorities did not immediately offer a motive for the rampage, but said they believed the gunman had acted alone. 

Witnesses said he entered a reception area of the college at mid-morning and opened fire before walking into one of two classes in session and spraying the room with bullets.

Paul Singh, whose 19-year-old sister Devinder Kaur was shot in the arm during Monday's rampage, told Reuters that according to his sister, the man was a former student at the college who showed up to class for the first time in four months.

"'Get in line and I'm going to kill you all,' is what he said this morning, my sister told me. They thought he was joking at first,'" Singh said.

Tashi Wangchuk said his wife, 28-year-old Dechen Yangzom, was in the second classroom. Wangchuk said she turned off the lights and locked the door when she heard gunfire.

"The guy came and banged on the door and shot several rounds at the door and then he left," Wangchuk told Reuters.

Oakland police spokesman Johnna Watson said seven people had been killed and three others wounded. It was the deadliest outburst of gun violence at a U.S.
school since a Virginia Tech student shot and killed 32 people and himself in a 2007 massacre on that campus.

Images from local TV stations showed frightened students and staff running from the school, located in a light industrial area near Oakland International Airport, as police and SWAT teams carrying assault rifles surrounded the area.

Hours later, two bodies remained on a grassy area outside the school, covered by yellow plastic sheeting.  Agents from the U.S. Bureau of Alcohol, Tobacco and Firearms were on the scene, along with dozens of local police.

Angie Johnson, 52, told the San Francisco Chronicle newspaper she was doing errands nearby when she saw a young woman run from the college with a bloodied right arm, crying "I've been shot, I've been shot."     

Johnson said the wounded woman told her the shooter was a man in her nursing class who shot one person at point blank range before spraying the room with bullets. Nearby business were evacuated and shut down for the day as officers searched the school and surrounding area. A spokeswoman for nearby Highland Memorial Hospital declined to comment on the condition of the victims being treated there.

"As you may have heard, the suspected shooter in today's deadly shooting at Oikos University on Edgewater Drive is in custody, and it appears he acted alone," the city said in a brief statement. - Reuters