The shooter has been identified by multiple government sources as Army Specialist Ivan Lopez.
Fort Hood, which remained locked down at 8:30 p.m., reported that there were multiple injuries after the shooting. However, Fort Hood officials said the number of people injured had not been confirmed.
There are believed to be 14 people injured in the shooting, according to law enforcement officials.
David Ross, a Fort Hood official, said the site is fully locked down and “completely sealed” as they search every building.
“There is a confirmed shooting that occurred,” Ross said. “We’re still trying to identify what we have.”
Secretary of Defense Chuck Hagel called the Fort Hood shooting a “terrible tragedy.”
Lopez reportedly killed himself and, according to CBS, he's among the four dead.
President Obama is expected to speak about the shooting soon. So far the White House's official statement is that the president is closely following the developments out of Fort Hood and promises to get to the bottom of what happened.
You'll of course remember that in 2009, Fort Hood was the scene of a shooting rampage that left 13 people dead and 32 more wounded. It was the worst mass-murder at a military installation in U.S. history. The man behind it, Army psychiatrist Nidal Hasan, was sentenced to death last year for the shooting.
Update: 11:20PM ET
The latest on Ivan Lopez: he's 34-years-old. He used a .45 caliber semi-automatic handgun during the shooting spree and to kill himself, apparently.
He reportedly worked as a truck driver for the Army and opened fire at the motor pool.
He was diagnosed with PTSD and was being treated for it after serving in Iraq. He arrived at Fort Hood less than two months ago.
More to come.