The man said he saw a soldier jumping over a fence and running away, but it was not clear whether that solider may have been the shooter.
Emergency crews from several surrounding communities headed to the base, home of the Army's 1st Cavalry Division.
Ford Hood near Killeen in central Texas was the site of a mass shooting Nov 5, 2009, when Major Nidal Malik Hasan, an Army psychiatrist, opened fire at a soldier readiness centre on the base.
He shot 13 people dead and wounded more than 30 others in what was the worst shooting ever to take place on an American military base.
Hasan, 43, who who said he was driven by a hatred of the wars in Iraq and Afghanistan, was left paralysed when he was shot by police responding to the shooting spree. He has been sentenced to death for the rampage.
