There were conflicting reports on the number of dead and wounded in the shooting rampage at Umpqua Community College in Roseburg, which began shortly after 10:30 a.m. local time.
The state's attorney general, Ellen Rosenblum, told the local NBC affiliate that 13 people had been slain and 20 wounded. Rosenblum's office did not return calls from Reuters seeking comment.
Governor Kate Brown said the suspect was a 20-year-old man but he was not identified further by authorities. CNN reported that four guns belonging to the shooter were recovered from the scene.
The massacre is the latest in a series of mass shootings at U.S. college campuses, movie theaters, military bases and churches in recent years. The killings have fueled demands for more gun control in the United States, where ownership of firearms is protected by the Second Amendment of the U.S. Constitution, and better care for the mentally ill.
President Barack Obama, speaking just hours after the rampage, said the mass killing should move Americans to demand greater gun controls from elected officials.
"Somehow this has become routine," a visibly angry and shaken Obama said. "The reporting is routine. My response here, at this podium, ends up being routine. ...We’ve become numb to this."
Kortney Moore, 18, told the local News Review newspaper that she was in her writing class in Snyder Hall when a gunshot came through the window and struck her teacher in the head.
Moore said the gunman told people to get on the ground, then asked them to stand up and state their religion before he started shooting.
Student Cassandra Welding told CNN that she heard 35 to 40 shots.
Student Brady Winder, in a posting on Facebook, said he was in a classroom in Snyder Hall, next door to the room where the shooting began and ran, along with his classmates, when they heard the gunfire.
"I ran to the edge of the campus, down a hill and waited. From talking with a student in the classroom where it happen, almost every person in the room was shot by a man with four guns," Winder wrote.
"I'm still shaken up ... I can't wrap my mind around this. Please just pray for the families and parents of these students," he posted.
PeaceHealth Sacred Heart Medical Center emergency room doctor Hans Notenboom told reporters three patients were flown to the hospital in Riverbend by helicopter, and two were moved directly into operating room.
The hospital said in a statement that the three victims were women between the age of 18 and 34.
Survivors were transported to a local fairgrounds and some family members were left waiting for hours to see if their loved ones would be among them.
"We have grief counselors waiting for those parents who have no children getting off that bus," said the college's president, Rita Calvin.
The college, which began its fall term this week and serves more than 13,000 students, 3,000 of them full-time, said it would be closed until Monday.
Agents from the Federal Bureau of Investigation and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were on their way to Roseburg.
Recent episodes of gun violence in the United States include the massacre of nine people at a South Carolina church in June and the killing of five U.S. servicemen in Chattanooga, Tennessee.
In 2012, seven students at the small Christian college Oikos University in Oakland, California, were shot dead by a former student, marking the deadliest outburst of violence at a U.S. college since April 2007, when a student at Virginia Tech University killed 32 people and wounded 25 others before taking his own life.