ATLANTA - A Georgia sheriff said officers were "desperately" searching Tuesday for two inmates who somehow got through a gate inside a prison bus, killed two guards and got away.

"My biggest worry is they're going to kill somebody else," Putnam County Sheriff Howard Sills said.

The two men overpowered and disarmed the guards about 6:45 a.m. as 33 inmates were being driven between prisons, Sills told reporters. One of them fatally shot both guards, and then they jumped out of the bus and carjacked a driver who happened to pull up behind them on a rural highway, Sills said.

"We are still desperately looking for these two individuals. They are armed with 9 mm pistols that were taken from these correctional officers. They are dangerous beyond description. If anyone sees them or comes into contact, they need to call 911 immediately," the sheriff said.

Multiple agencies have contributed to a reward of $60,000 for information leading to the arrests of the two inmates, Georgia Bureau of Investigation spokeswoman Nelly Miles said.

The fugitives - Donnie Russell Rowe, serving life without parole, and Ricky Dubose, who has elaborate tattoos on his face and neck - carjacked a "grass green," four-door 2004 Honda Civic with the Georgia license plate number RBJ-6601.

Sills said the two inmates got a head start by taking and tossing the Honda driver's cellphone and leaving the other 31 prisoners locked inside the bus on state Highway 16.

Later Tuesday, the manhunt shifted about 25 miles north to the city of Madison, where two men fitting their description were seen entering a Family Dollar store less than a mile from a house that was burglarized. Sills said the men then vanished again, and authorities have no reason to believe they have split up.

"If I knew where they were, I would not be talking with you," Sills said at a news conference.

The sheriff cut off more questions, saying, "All right guys, we gotta go hunt."

The slain guards were identified as Sgt. Christopher Monica and Sgt. Curtis Billue, both transfer sergeants at Baldwin State Prison. Monica had been with the Georgia Department of Corrections since October 2009 and Billue since July 2007.

Sills was emotional as he described the scene.

"I saw two brutally murdered corrections officers, that's what I saw," he said. "I have their blood on my shoes."

How the two inmates managed to reach and overpower the guards remains under investigation, Sills said.

"They were inside the caged area of the bus," he said. "How they got through the locks and things up to that area, I do not know."

Protocol is to have two armed corrections officers on the bus, but the officers don't wear bullet-proof vests during transfers, Corrections Commissioner Greg Dozier said.

"We lost two of our fellow officers, two of our kin. We see our officers as our family," Dozier said.

Monica was 42 and leaves behind a wife, Dozier said. Billue was 58 and is survived by his father, five sisters, two brothers and two sons, said Jim Green, an attorney speaking for the Billue family.

"Officer Billue's family asks for prayers for all of those who are now placing their own lives at risk to bring these men to justice and asks anyone who has information that may assist in apprehending these perpetrators to please contact law enforcement," Green said in an email.

The guards were moving the inmates to a diagnostics center in Jackson, where their next placement was to be determined, Dozier said, adding that inmates do not know their transfer dates ahead of time.

U.S. Deputy Attorney General Rod Rosenstein said federal resources are being committed to help catch the fugitives. The FBI and U.S. Marshals have joined the investigation, Sills said.

"An attack on any American law enforcement officer is an attack on every American law enforcement officer and the principles we all believe in," Rosenstein told a Senate budget panel in Washington on Tuesday morning.

Both escaped inmates are serving long sentences for armed robbery and other crimes. The Department of Corrections said Rowe, 43, has been serving life without parole since 2002, and Dubose, 24, began a 20-year sentence in 2015.

A photo released by the sheriff's office in Elbert County, the site of his most recent conviction, shows Dubose with prominent tattoos. He appears to have a crown tattooed above his right eyebrow, writing above his left eyebrow and large letters covering the entire front of his neck.

"They need to surrender before we find 'em," Sills said.