"There is no indication that this incident is related to terrorism," Lieutenant General Mark Milley told reporters, adding that 16 people were wounded in the incident at Fort Hood, scene of a deadly shooting rampage in 2009. The shooter took his own life, Milley said.
President Barack Obama said he was "heartbroken something like this might have happened again," after a shooting at the base which killed 13 people five years ago.
The sprawling military site remained on lockdown a couple of hours after staff were ordered to shelter in place, after emergency crews rushed to the scene.
A soldier told CNN he heard gun shots "and assumed they were blank rounds... We then heard a burst, another burst and it was clear they weren't blank rounds. They were live rounds."
Obama, who was in Chicago, said investigators would "get to the bottom of what happened."
"Obviously, this reopened the pain of what happened at Fort Hood five years ago," Obama said.
"Many of the people there have been on multiple tours of Iraq and Afghanistan, they served with valour, they served with distinction. At their home base they need to feel safe."
On November 5, 2009, Major Nidal Hasan opened fire at a medical facility in the sprawling base that serves as a staging point for soldiers to deploy to combat zones.
Twelve of the 13 dead and 30 of the wounded were soldiers. Hasan was himself shot by a civilian police officer who responded to the attack and Hasan is now partially paralysed.
A military jury last August sentenced the US-born Muslim of Palestinian descent to death.
Fort Hood is spread out over almost 900 square kilometres, and is the largest US military base with a population of 70,000 including 42,000 military personnel.
Fort Hood is spread out over almost 900 square kilometres, and is the largest US military base with a population of 70,000 including 42,000 military personnel.
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