US President Barack Obama has ordered flags be flown at half-mast in honour of the victims of the mass shooting at an Oregon community college.

The order applies to flags at the White House, public buildings, US military installations and naval vessels, government facilities and US embassies abroad.

Authorities say a 26-year-old gunman opened fire on Thursday in a class at the college, killing nine and injuring nine others before he himself was shot dead

Police discovered six weapons and body armour at the scene.

A police search found another seven weapons inside the apartment of the shooter Christopher Harper-Mercer who was a student at the Umpqua Community College where the shooting took place.

US correspondent Jack Tame reports police are still working to find a motive.

"Although not a lot is known about his background, as seems fairly typical in these circumstances, fellow students have described him as
a bit of a loner, a bit of an outsider.

Tame said Douglas County Sheriff John Hanlin chose not to release the name of Harper-Mercer in his media conference, following the shooting at Umpqua Community College in Roseburg.

"He hasn't supported stronger gun laws in the United States, but in saying that he's also refusing to name the gunman, he says you can find his name in headlines around the world but neither he or any of his staff will be giving the gunman any glory by naming him."

Meanwhile UN Secretary-General Ban Ki-moon says he's deeply saddened to learn of the latest mass shooting and has urged the United States to take action to curb gun violence, saying it's taking an appalling toll on American society.