At least 12 people were killed at Fort Hood military base in Texas on Thursday, including one gunman, the facility's commander said.

Lieutenant General Robert Cone said the killing spree began at around 1:30 pm local time, when at least one soldier opened fire on fellow troops at the base, one of the world's largest military facilities.

"At this time, we are looking at 12 dead and 31 wounded," Cone said in a statement broadcast on CNN.

The toll included one gunmen, but Cone said more suspected shooters were later caught.

"We since then have apprehended two additional soldiers who are suspects."

"They tracked the suspected individuals to an adjacent facility, and they were apprehended. They are soldiers, but they are suspects at this time, and we are looking at that."