"There has been a shooting at Fort Hood and injuries are reported. Emergency crews are on the scene. No further details are known at this time," the Army post said in an evening statement.
Fort Hood's official Twitter feed asked that all personnel on post shelter in place. Sirens were going off.
President Barack Obama has been briefed on the incident and will continue to receive updates, according to a White House press pool report. Defense Secretary Chuck Hagel also was monitoring the situation.
Deke Jones, with Scott & White Memorial Hospital, told CNN his facility was receiving patients.
"I don't have a number," he said.
Sheriff's deputies from Bell County and state troopers are assisting by securing the area around the post, according to Bell County Sheriff's Lt. Donnie Adams.
Authorities in the town of Killeen, just outside the gates, are also standing by to help, said Mayor Dan Corbin.
"It is unclear what is going on right now," Corbin said. "We have been in touch with appropriate personnel, we are standing by with our police and ambulances, if needed. We are very concerned. Fort Hood is always there for us and we want to be there for them."
He continued: "They are used to dealing with combat situations, and I'm sure they are very capable of handling this."
Police in nearby Waco advised those on post to stay away from windows and to keep doors closed and locked.
"Injuries are being reported. Be AWARE!! If you are in the Ft. Hood Post area there is an on-going active shooter," the department tweeted.
