"Initially, I thought it was a training exercise," he told the Fort Hood Sentinel.

"A soldier came running past me and said: 'Sir, there is someone shooting.'

"As he ran past me, I saw blood on his back. I don’t think he even knew he had been shot."

All the dead were killed in the initial shooting at the processing centre, Lieutenant General Cone said. Local media had reported that at least one of the locations where the shootings took place was frequented by family members of soldiers.

Lieutenant General Cone said no children were among the dead but one was a civilian policeman.

Gunman's family stunned

The alleged gunman's cousin, Nader Hasan, said Major Malik was opposed to the wars in Afghanistan and Iraq after hearing the stories of returning servicemen.

But the shooting had stunned the family, he said.

"We are trying to make sense of all this," Nader Hasan told Fox News. "He wasn't even someone who enjoyed going to the firing range."

"He was dealing with some harassment from his military colleagues," Nader Hasan said.

"I don't think he’s ever been disenchanted with the military," he said of his cousin. "It was the harassment."

Nader Hasan said his cousin was born and raised in Virginia and graduated from Virginia Tech University. He was raised a Muslim and went into the military against his parent's wishes.

The wounded were taken to hospitals in Texas. A number of ambulances were shown on local TV leaving the base with their sirens blaring.

The Scott & White Memorial Hospital, in Temple, Texas, updated its website to say it was receiving victims from the army base who were "suffering from gun shot wounds".

"Due to the recent events on Fort Hood, we are in URGENT need of ALL blood types," a statement from the hospital read.

Fort Hood

Fort Hood is the largest US military base in the world and had been working to rehabilitate many soldiers suffering from post-traumatic stress syndrome, local congressman John Carter told MSNBC.

Fort Hood is the headquarters of the Army 3rd Corps, the 4th Infantry Division and the 1st Cavalry Division. All those units have seen extensive duty in Iraq and Afghanistan.

The website of the base in central Texas posted an alert that says: "Effective immediately. Fort Hood is closed. Organisations/units are instructed to execute a 100 per cent accountability of all personnel. This is not a drill. It is an emergency situation."

In May 2007, five men suspected of being Islamic militants were arrested by the FBI as part of a plot to attack the US base in Fort Dix, New Jersey. Four were sentenced in April to life imprisonment and the fifth to 30 years.

Horrific: Obama

Using a scheduled press conference after meetings with native American leaders, Mr Obama vowed to "make sure we get answers to every single question about this horrible incident".

Mr Obama said he had met Defence Secretary Robert Gates and the head of the joint Chiefs of Staff Admiral Mike Mullen and was being kept up to date by the Pentagon and the FBI.

"My immediate thoughts and prayers are with the wounded, and the families of the fallen, and those who live and serve at Fort Hood," he said.

"These are men and women who have made the courageous decision to risk and at some times give their lives," he said.

"It’s difficult enough when we lose these brave Americans overseas. It is horrifying that they should come under fire at an army base on American soil.

"As commander in chief, there is no greater honour, but also no greater responsibility for me than to make sure the extraordinary men and women in uniform are properly cared for, and that their safety and security when they are at home is provided for," he said. "We are going to stay on this."

Resident's Twitter posting

Bridget Donovan, a resident on the base, described her terror as the emergency unfolded.

"locked in my post housing. scared. dont know where the shooters are," she wrote on Twitter.

"all i hear are sirens telling us to stay indoors. can't hear any gunfire.

"i'm safe, but scared. i have my husband and many friends on post. worried about them."

Schools in the area were also on lock-down, MSNBC said.

Fatal Baghdad shooting in May

In May, a US soldier was charged with murder after he allegedly shot dead five colleagues at an army base in Baghdad.

In interviews, Sergeant John Russell's family described him as a kind-hearted man who so loved his country that he joined the military.

However, Seargent Russell's father wondered whether his son snapped under questioning by counsellors, or feared that his career was over.

A criminal investigation is under way.