THE GUNMAN who killed nine people in America's latest mass shooting had a stockpile of more than a dozen weapons, authorities have confirmed.

Chris Harper Mercer was armed with six guns when he arrived at Umpqua Community College in Roseburg, Oregon, 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.

His social media profiles suggested he took an interest in other mass shootings.

He wrote "The more people you kill, the more you're in the limelight."

President Barack Obama has since called on Americans to press their politicians to support reform.

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

Meanwhile, reports in American suggest the gunman handed a box to a survivor during the shooting.

According to Stacy Boylan, whose daughter Anastasia was injured in the shooting, the gunman "gave somebody a box, somebody who lived, and said, 'You gotta deliver this'."

Boylan said he doesn't know what was in it.

Authorities confirmed the shooter handed out something during the shooting, but could not confirm what the item was.

In 2008, Mercer enlisted in the army, but was discharged just weeks into his training.

It is unclear why he was discharged.

Speaking about the killings, his father, Ian Mercer, said he was "just as shocked as everybody" by his son's actions.