The gunman who killed nine people in a shooting rampage at a college in Oregon had 13 weapons, federal agents said.

Dressed in a flak jacket, Chris Harper Mercer brought six guns to Umpqua Community College in Roseburg and opened fire on Thursday morning.

He was killed by police in a gun battle and another seven weapons were found at his home. All 13 were bought legally.

Police have released the names of the victims, who ranged in age from 18 to 67. The oldest was a teacher.

Survivors have been telling their stories.

Medicine student Sharon Kirkham told the BBC her friend Kim died in her arms after being shot three times.

"I heard her gasping for air, but I couldn't save her," she said.

President Obama reiterated his anger at gun violence at a press conference on Friday, calling on the public to press their politicians to support reform.

"You've got to be a single issue voter on this, because that's what happening on the other side," he said, referring to the National Rifle Association's lobbying power.

Obama said the NRA were "effective but don't represent the American people".

Mercer was described as a troubled man by others. Photo: BBC/Reuters.

Mercer enlisted in the army in 2008, but was discharged after less than a month in basic training, for reasons unknown.

It is unclear why he carried out the killings. Two victims have said religion was an issue - the gunman asked his victims to state their religion and shot dead the Christians.

His father, Ian Mercer, said he was "just as shocked as everybody" by his son's actions.

People in the tight-knit community of Roseburg have been lining up all day to give blood at a specially organised blood drive.

"My cousin Becky works in the science department and was in the building next door to where it happened.

"She was on lockdown for an hour and said it was terrifying. Giving blood is the least we can do," said 30-year-old Abby Watson.

Tanya Talbot, 22, felt similarly compelled.

"My best friend's sister is in surgery. She's expected to be OK, but I had to do something. It doesn't seem real," she said.

In an online profile appearing to belong to the gunman, he listed hobbies including the internet and "killing zombies", described his politics as "conservative, Republican" and said he was spiritual but not religious.

His social media profiles also suggested he took a keen interest in other mass shootings.

"The more people you kill, the more you're in the limelight," he said in one post, referring to Vester Flanagan, who shot and killed two journalists during a live broadcast in Virginia in the summer.

Local police in Douglas, Oregon, have refused to say the gunman's name because they say it will only encourage others.

Many online discussions about the killings have preferred to focus on Chris Mintz, a student and army veteran who is recovering after taking seven bullets while trying to stop the gunman.