Police investigating a mass shooting at an Oregon college say the gunman had access to a deadly arsenal of 13 weapons.

Chris Harper-Mercer killed nine people as he carried out his rampage at the Umpqua Community College in Roseburg.

The 26-year-old man ordered students to stand up and state their religion before firing. He later died in a shoot-out with officers.

Police have recovered six weapons from the scene of the attack, including at least three pistols and a rifle, and another seven at his home.

They said all were purchased legally, some by Harper-Mercer and others by his family.

Authorities have appeal for information from the public about the deadly shooting, including any video footage or photographs they have of the incident.

Harper-Mercer was said to have been born in England before moving to the United States as a young boy.

Investigators believe he may have been a student at the college because a receipt found at the scene showed he bought textbooks from the campus bookshop two days before the shooting.

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

The bullet hit her teacher in the head, throwing him to the ground, before the gunman stormed in.

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

If students replied that they were Christian, he replied: "Good, you'll see God in a second."

The names of the victims have not been officially released but some people have expressed fears on social media that their loved ones, including Lucero Alacraz and Rebecka Carnes, may been among the dead.

Harper-Mercer's social media profiles featured content supporting the IRA.

According to his profile on a dating site, he is 'mixed race,' a 'conservative Republican,' 'not religious' and lived with his mother.

The gunman's father, Ian Mercer, said he was "shocked" and "devastated" by the attack.

Speaking to reporters, he said: "Obviously, it's been a devastating day. Devastating for me and my family.

"I'm just as shocked as everybody at what happened today. I've just been talking to the police and the FBI."

The massacre is the deadliest shooting in the US since nine people died in a rampage at a South Carolina church in June.

President Barack Obama called for stricter gun control laws in America to stop the violence.

He said "inaction" on gun control legislation makes all Americans "answerable" for the ongoing gun violence.

"We are going to have to change our laws. This is not something I can do by myself," he said.