Barack Obama said the US was becoming numb to mass shootings after a gunman killed up to a dozen people at a rural Oregon college, before dying in a shoot-out with police.
The president was visibly angry as he spoke to reporters hours after the attack, saying that the shooters have "sickness" in their minds.
Police began receiving calls about a campus shooting at Umpqua Community College at 10.38am local time.
The killer, identified only as a 20-year-old man, invaded a classroom and demanded that people stand up and state their religion before spraying more bullets, one student reported.
The authorities shed no light on the gunman's motive and said they were investigating.
State police Lieutenant Bill Fugate said that at least 20 others were hurt in the attack in the small timber town of Roseburg, about 180 miles south of Portland.
"It's been a terrible day," a grim-faced Douglas County Sheriff John Hanlin said at a news conference. "Certainly this is a huge shock to our community."
Mr Obama repeated his support for tighter gun-control measures, and said thoughts and prayers are no longer enough in such situations because they do nothing to stop similar attacks from happening a few weeks or months later.
He challenged people wanting to confront the problem to vote for elected officials who will act.
"I'd ask the American people to think about how they can get our government to change these laws and to save lives and to let young people grow up, and that will require a change of politics on this issue," he said.
The president said there is a gun for roughly every man, woman and child in the US.
"I hope and pray that I don't have to come out again during my tenure as president to offer my condolences to families in these circumstances.
"But based on my experience as president, I can't guarantee that. And that's terrible to say."
