An angry President Barack Obama appeared in the White House briefing room on Thursday to say that "prayers are not enough" in addressing another horrific mass murder in a US campus, this time in Oregon where a gunman specifically targeting Christians opened fire, killing nine people and wounding seven others before police shot him to death.

Wearing a grim expression, Obama said it was not enough to offer prayers after major shootings continued to occur regularly throughout the country, reports said.

"As I said just a few months ago, and I said just a few months before that, and I said each time we see one of these mass shootings, our thoughts and prayers are not enough," Obama told reporters.

"It's not enough," he repeated.

Obama once again harped on the need for stricter gun laws, calling on gun owners who use weapons for hunting, sport and protection to question whether the gun lobby represented their views. However, he did not directly mention the National Rifle Association, an organisation that has broad political influence in Washington.

Obama said it is clear that people who commit such heinous crimes had a "sickness in their minds."

"But we are not the only country on Earth who has people with mental illnesses who want to do harm to other people," he said. "[But] we are the only advanced country on Earth who sees these kinds of mass shootings every few months."

The gunman, identified as Chris Harper-Mercer, 26, barged into a classroom full of screaming students, at Umpqua Community College in Roseburg, Oregon, on Thursday, firing dozens of shots, witnesses said.

According to survivors, the assailant—who CNN said was armed with three handguns, a "long gun" and body armour—at one point ordered students to stand up and state their religion before shooting them one by one.

One of the students was an 18-year-old woman who was wounded but survived by playing dead. Her father, Stacy Boylan, told CNN his daughter told him she saw the gunman shoot her professor point blank on the head.

"He was able to stand there and start asking people one by one what their religion was," Boylan said, recounting what his daughter told him. "'Are you a Christian?' he would ask them. ... 'If you're a Christian, stand up. Good. Because you're a Christian, you're going to see God in just about one second,' and he shot and killed them. And he kept going down the line doing this to people."

Another student who witnessed the carnage, Kortney Moore, 18, also issued a similar statement.

Thursday's school shooting was the deadliest this year, surpassing the nine fatalities in a gun battle between motorcycle gangs in Waco, Texas, in May, and the nine people inside a black church in Charleston, South Carolina, who were gunned down by a white assailant in June.

Before Thursday's incident, 293 mass shootings have already been reported this year, according to the Mass Shooting Tracker website.

In April 2007, a student at Virginia Tech University in Blacksburg killed 32 people and wounded 25 before taking his own life.

Obama was the target of angry online posts after Thursday's deadly shooting. One of the tweets came from former CNN host Piers Morgan, a native of Britain known for his fierce criticism of America's constitutional gun rights. "Shame on you, Mr President@BarackObama – in 6yrs, you've done absolutely nothing to stop these gun massacres happening. NOTHING. #oregon."

Actress and director Rose McGowan tweeted: "Oh my god, Oregon State. When will this stop? This is madness. We must stop the NRA & its choke."

Comedian Michael Ian Black wrote via Twitter: "Another massacre. Don't wait to talk about it. Gun control now."

At a campaign stop in Boston, Democratic presidential front-runner Hillary Clinton called for "sensible gun control measures."

Republican presidential candidate Ben Carson took a different view in an interview with radio host Hugh Hewitt, insisting more gun control is not the answer.

"Obviously, that's not the issue," he said. "The issue is the mentality of these people and we need to be looking at the mentality of the individuals and seeing if there are any early warning clues that we can gather that will help us as a society to be able to identify these people ahead of time."