PHOENIX -- A Glendale Army mom said she went into panic mode when she first learned a gunman had opened fire in Fort Hood -- the same military base where her 20-year-old son is stationed.

• Watch: Army Mom Rattled After Fort Hood Shooting
• Raw Video: First Images From Scene

Authorities said an Army psychiatrist set to be shipped overseas opened fire at the facilities on Thursday, killing 13 people and wounding 30 others. The violence was believed to be the worst mass shooting in history at a U.S. military base.

Nikki Colletti said she called her son, Anthony, in the wake of the shooting rampage but he did not answer the phone.

"So I then went and called his buddy," Colletti said. "I said, 'How are you guys?' and he said, 'We're OK.' I texted him back and said, 'How's everybody else?' and he said, 'Not good.'"

Colletti said she still doesn't know the status of the others in Anthony's platoon and whether his comrades are among the dead.

She said her son has been stationed in Fort Hood since February and is scheduled to deploy to Afghanistan in two months. She said she never worried about Anthony's safety on base.

"That's a place where you would think they would be safe," she said. "That's their home. That should be their fortress."

Video from the scene showed police patrolling the area with handguns and rifles, ducking behind buildings for cover. Sirens could be heard wailing while a woman's voice on a public-address system urged people to take cover.

Colletti said her main concern is for the emotional health of her son. She said she's hoping his platoon will be able to get some much needed counseling before he is deployed in January.

Arizona Guard Soldiers OK

A group of Arizona national guard soldiers at the base are all accounted for. They are part of the 158th Combat Sustainment Support Battalion. Eighty-six men and women make up the group.

They are currently taking part in mobilization training before being deployed to Afghanistan in January.

Only one of Arizona's four major military bases raised their security levels after the attack. Officials at Luke Air Force Base in Glendale, Davis-Monthan Air Force Base in Tucson and Fort Huachuca in Sierra Vista said they were monitoring the situation but not making any changes. It was different at the Marine base in Yuma.

"The bottom line for us is that we are increasing security at our gates because the threat hasn't yet been defined, and we're reminding our Marines to be vigilant in their areas of responsibility," said Capt. Rob Dolan, public affairs officer for the Marine Corps Air Station, Yuma.

Suspected Gunman Is Alive

The shooting began around 1:30 p.m., Lt. Gen. Bob Cone said at a news conference. He said all the casualties took place at the base's Soldier Readiness Center, where soldiers who are about to be deployed or who are returning undergo medical screening.

"It's a terrible tragedy. It's stunning," Cone said.

Authorities said immediately after the shootings that they had killed the suspected shooter, Army Maj. Nidal Malik Hasan, but later in the evening they recanted and said that he was alive and in stable condition at a hospital, watched by a guard.

The soldier used two handguns, Cone said. It was not clear if the gunman had stopped to reload.

Covering 339 square miles, Fort Hood is the largest active duty armored post in the United States. Home to about 52,000 troops as of earlier this year, the sprawling base is located halfway between Austin and Waco.

The facility officially opened on Sept. 18, 1942, and was named in honor of Gen. John Bell Hood. It has been continuously used for armored training and is charged with maintaining readiness for combat missions.

The attack happened just down the road from one of the worst mass shootings in U.S. history. On Oct. 16, 1991, George Hennard smashed his pickup truck through a Luby's Cafeteria window in Killeen, Texas, and fired on the lunchtime crowd with a high-powered pistol, killing 22 people and wounding at least 20 others.

No other shooting at a military base in the U.S. has been anywhere near as deadly as Thursday's. In 1993, a gunman at Fort Knox shot five civilian co-workers, killing three, and then fatally shot himself.