Police have killed a 20-year-old gunman at a college in rural Oregon after a rampage that left at least 13 people dead.

Douglas County Commissioner Chris Boice confirmed the death toll at Umpqua Community College.

He told Sky News one of the victims was a female shot in the chest at the school in Roseburg, 180 miles (290km) south of Portland.

Douglas County Sheriff John Hanlin said more than 100 police officers responded and "neutralised" the male attacker after a shootout.

State police Lt Bill Fugate told KATU-TV there were at least 20 injured.

The attacker went from class to class, opening fire, according to local media.

Student Kortney Moore, 18, told the News Review newspaper she was in her class in Snyder Hall when a shot came through a window.

She said the gunman told people to get on the ground before ordering them to stand up and state their religion, then he opened fire.

Oregon Governor Kate Brown, who confirmed the gunman's age, said: "My thoughts are with the families and victims."

Douglas County Sheriff's office said the incident was reported at about 10:38am local time on Thursday.

Umpqua student Brady Winder, who was in a nearby class, said they heard a sound like a heavy object dropping.

The 23-year-old said: "Everybody's head turned and looked at each other, trying to just grasp what was happening, and someone said, 'Those are gunshots.'

"We heard people screaming next door. And then everybody took off. People were hopping over desks, knocking things over."

He said he saw a girl swim across a creek while escaping.

State police said there was believed to be only one shooter "who is no longer a threat".

Authorities patted down students at the scene to check no other gunman was at large.

Joe Olson, the former president of the college, said it has only one unarmed security officer on duty at any time.

The adult-learning college has some 3,300 students and the average age of students is about 38, according to its website.

Agents from the FBI and the Bureau of Alcohol, Tobacco and Firearms are among those who responded to the scene.

The White House says President Barack Obama is being briefed about the latest US mass shooting.

According to pro-firearms control group Everytown for Gun Safety, it is the 142nd school shooting since the attack at Sandy Hook Elementary, Connecticut, in December 2012.