There were conflicting reports on the number of casualties and wounded at Umpqua Community College.
The state’s attorney general told the local NBC affiliate that 13 people had been slain, 20 wounded and the gunman was killed.
The suspect was not identified but CNN reported it was a man in his late 20s.
Douglas County Commissioner Chris Boice said the shooting left about 30 casualties, but he could not immediately say how many of those people died and how many were injured.
The shooting is the latest incident of gun violence in the US, raising demands for more gun control and more effective treatment of the mentally ill.
Recent episodes of gun violence include the massacre of nine people at a South Carolina church last spring and the killing of five US servicemen in Chattanooga, Tennessee.
CNN reported that one of the wounded was a female who had been shot in the chest. The Oregonian said that at least six patients were critically injured, citing an official with Life Flight.
The Douglas County Sheriff’s office said on Facebook that officers had responded to a shooting at the college following 911 calls at 10.38am local time.
Mercy Medical Centre in Roseburg said on Facebook that the hospital had received nine patients from the shooting. Media reported authorities were combing the campus, which serves more than 13,000 students, 3,000 of them full-time. Autumn term began at the college on Monday.
The Douglas County Sheriff’s Office said students and faculty members were being bused to the nearby fairgrounds where they could be picked up.
President Barack Obama was briefed on the shooting by Lisa Monaco, his homeland security adviser, a White House official said. The FBI said agents were responding from offices in Medford, Eugene, Salem and Portland.
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 US college since April 2007, when a student at Virginia Tech University killed 32 people before taking his own life.