The incident occurred Wednesday afternoon at Fort Hood, the site of a notorious 2009 mass shooting.
Law enforcement sources said four people were killed, including the gunman, who died of a self-inflicted wound. Authorities said 11 other people were wounded, some of them seriously.
Sources told CBS News the shooter had been identified as 34-year-old soldier Ivan Lopez. A source said the violence apparently stemmed from some sort of soldier dispute.
In Chicago, President Barack Obama said he was following the situation closely.
“Any shooting is trouble. Obviously, this reopens the pain of what happened Fort Hood five years ago,” the president said.
“We’re heartbroken that something like this might have happened again,” Obama said. “I want to just assure all of us we are going to get to the bottom of exactly what happened.”
“It’s a terrible tragedy, we know that. We know that there are casualties, both people killed and injured,” Secretary of Defense Chuck Hagel told reporters in Honolulu, Hawaii, where he was meeting with Asian defense ministers.
Warning sirens went off around 4:25 p.m. and all personnel were urged to shelter in place as the base went on lockdown.
“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 post said in a brief statement.
A man who said he was a witness told CBS affiliate KWTX that about 20 shots were fired at a post motor pool. 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.
Officials at Baylor Scott & White Health said Wednesday evening that the hospital was treating four patients and that two others were en route. The patients had injuries to the chest, neck and extremities. Their conditions ranged from stable to quite critical, officials said.
First responders from surrounding communities headed to the post, home of the Army’s 1st Cavalry Division.
Ford Hood near Killeen in central Texas was the site of a mass murder on Nov. 5, 2009, when Maj.Nidal Malik Hasan, an Army psychiatrist, opened fire at a soldier readiness center on the base. He shot 13 people dead and wounded more than 30 others. It was the worst shooting ever to take place on an American military base.Hasan, who was left paralyzed when he was shot by police responding to the shooting spree, has been sentenced to death for the rampage.
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, offered sympathies to the Fort Hood community on Wednesday night.
“Our thoughts and prayers are with the Fort Hood community in the aftermath of this tragedy. Many questions remain and our focus is on supporting the victims and their families,” Dempsey said. “This is a community that has faced and overcome crises with resilience and strength.”
Sen. John Cornyn, R-Texas, asked Americans to pray for the victims and their families.
“Tonight, Texans’ hearts are once again very heavy. The scenes coming from Fort. Hood today are sadly too familiar and still too fresh in our memories,” he said. “No community should have to go through this horrific violence once, let alone twice.”