The killer, identified only as a 20-year-old man, invaded a classroom and demanded that people stand up and state their religion before spraying more bullets, one student reported.
Authorities shed no light on the gunman's motive and said they were investigating.
Oregon Attorney General Ellen Rosenblum said 13 people were dead after the attack at Umpqua Community College in Roseburg, about 180 miles south of Portland. It was not immediately clear whether that number included the gunman. State police Lt. Bill Fugate told KATU-TV that at least 20 others were hurt.
Kortney Moore told the Roseburg News-Review newspaper that she was in a writing class when a shot came through a window. The gunman entered her classroom and told people to get on the ground. The man then started asking people to stand up and state their religion and opened fire.
Lorie Andrews, who lives across the street from the campus, said she heard what sounded like fireworks followed by sirens. She walked up the road and spoke to students who had streamed out.
"One girl came out wrapped in a blanket with blood on her," Andrews said.
Hours after the attack, a visibly angry President Barack Obama spoke to reporters, saying the U.S. is becoming numb to mass shootings and that the shooters have "sickness" in their minds.
Repeating his support for tighter gun-control measures, he said thoughts and prayers are no longer enough in such situations because they do nothing to stop similar attacks from happening a few weeks or months later.
Douglas County Sheriff John Hanlin said the gunman was killed during an exchange of gunfire with officers. The sheriff did not say whether the shooter was killed by officers or took his own life.
"We locked our door, and I went out to lock up the restrooms and could hear four shots from the front of campus," UCC Foundation Executive Director Dennis O'Neill told the Roseburg newspaper.
The school has about 3,000 students. Its website was down Thursday, and a phone message left at the college was not immediately returned.
Neither state police nor the sheriff's office returned calls from The Associated Press seeking details.
The sheriff's office reported on Twitter that it received a call about the shooting at 10:38 a.m. The local fire district advised people via Twitter to stay away from the school.
Later in the day, students and faculty members were being bused to the county fairgrounds, the sheriff's office said.
Former UCC President Joe Olson, who retired in June after four years, said the school had no formal security staff, just one officer on a shift.
One of the biggest debates on campus last year was whether to post armed security officers on campus to respond to a shooting.
"I suspect this is going to start a discussion across the country about how community colleges prepare themselves for events like this," he said.
Sutherland High School Principal Justin Huntley said some of his former students were in the room where the shooting took place.
The school made counselors available for students.
"It's a very somber day," Huntley said. "You take some deep breaths and you just try to get through it."
Roseburg Public Schools Superintendent Gerry Washburn said a large number of Roseburg High School students go straight to UCC after graduation.
"We are a small, tight community, and there is no doubt that we will have staff and students that have family and friends impacted by this event," he said.
The rural town lies west of the Cascade Mountains in an area where the timber industry has struggled. In recent years, officials have tried to promote the region as a tourist destination for vineyards and outdoor activities.
