This is a developing story.

Colt Gray, the alleged gunman who opened fire at Apalachee High School in Barrow County, Georgia, killed four people and injured at least nine Wednesday morning when he began shooting at innocent victims inside the school, police say.

At approximately 10:20 a.m., around two hours after classes at Apalachee had begun, the Barrow County Sheriff's Office responded to reports of an active shooter.

"Within minutes, law enforcement was on scene as well as two school resource officers assigned here to the school," Barrow County Sheriff Judd Smith told reporters during a press conference Wednesday afternoon. 

GEORGIA SCHOOL SHOOTING: LIVE UPDATES

"Once they encountered the subject, the subject immediately surrendered to these officers, and he was taken into custody."

Officials said the four victims killed were two students and two teachers. 

Surviving victims have been taken to local hospitals to be treated for various degrees of injury, according to law enforcement.

Gray, a 14-year-old student at Apalachee High School, will be charged with murder and prosecuted as an adult, according to Smith.

GEORGIA HIGH SCHOOL SHOOTING: 4 DEAD, 1 SUSPECT IN CUSTODY, AUTHORITIES SAY

Local law enforcement is coordinating both the investigation and charges with District Attorney Brad Smith of the Piedmont Judicial Circuit.

"The priority right now for us, within this investigation, is to gather all the facts," Smith said. "This is a murder investigation."

Georgia police have yet to release the identities of the victims.