Students at a US college in Oregon where 10 people were killed by a lone gunman on Thursday described scenes of panic and terror as they ran for their lives or hid in classrooms.

"I probably heard a good 35 to 40 shots," Cassandra Welding, who was in an adjacent room to the shooter, told local media.

She said a fellow student at Umpqua Community College in rural Roseburg opened a connecting door to check what was happening and was shot.

"Then we locked the doors, turned off the lights and ... we were all pretty much in panic mode and called 911 and our parents and (said) 'I love yous' because we didn't know what would happen, if those were our last words."

"We put our backpacks in front of us, chairs, whatever we could, to shield ourselves in case he came in," she added.

Student Brady Winder said he was in class on what was the fourth day of the school year when he heard a loud pop at around 10:40am from an adjoining classroom in Snyder Hall. He said he initially assumed it was a desk or someone hitting the floor.

Winder said his teacher called out through the door to see if everything was OK and then further shots rang out.

"Somebody said these are gunshots. We all froze and bolted out the door," he told local media. "I didn't really have any time to think. It was fight or flight."

Several students on the sprawling campus said they had no clue something was amiss until they heard police and ambulance sirens and the school was placed on lockdown.

"We thought it was just a drill maybe because we didn't hear any alarms or anything at first," said Luke Rogers.

"When we exited the building, officers made us put our hands on our head and go in a single-file line," he added. "As we passed Snyder Hall we could see the doors open and on the ground where the detectives had marks there were little drops of blood."

Others described scenes of panic.

"Students are running everywhere. Holy God," wrote Kayla Marie on her Twitter account.

Some students could be seen hugging and crying as they exited the school and were put on board buses that took them to the local fairgrounds where anxious parents and family awaited.

Authorities said they would not release the names of the victims for 24 to 48 hours.

The college has some 3,300 students and is located in a picturesque region of Oregon.