Family members of students and staff at Apalachee High School called 911 to find out about their loved ones after a mass shooting that left four dead unfolded on Sept. 4, newly released audio reveals.

The 911 call center in Barrow County was inundated after the shooting began at about 10:20 a.m., when authorities say 14-year-old Colt Gray began his rampage. Some callers were met with an automated message that there was "high call volume," according to the audio reviewed by USA TODAY.

"Sir, my daughter goes to the school next door to Apalachee. Is there a school shooter?" one caller said.

"We do have an active situation at Apalachee High School right now. We have a lot of calls coming in and we do have units on scene," a 911 operator responded.

Authorities also released audio of communications between officers on the scene as they cleared classrooms and discovered injured and deceased victims. In one recording, an officer describes applying a tourniquet to an injured female victim. "She's gonna need to get out of here pretty quick," he says.

Barrow County officials told USA TODAY that some 911 calls are exempt from being disclosed as public records if they contain the voice or cries of children.

"What is going on at the high school, at Apalachee High School," one man asked a 911 operator who said she could not confirm any information. "My son just texted me. He's a student in there right now, he says people are dying."

A man told a 911 operator that his daughter worked as a school psychologist at Apalachee and was working with a student in a trailer "next to where the shooting was happening." The man said his daughter tried to hide behind a desk with the student but "she’s upset because she can’t get the door locked."

"I want them to be aware that she’s in a trailer and she can’t lock the door and if they can check on the trailers... hopefully they can check it and get her out," he said.

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Over an hour after the shooting started, one call came from a woman who identified herself as Gray's aunt and said she was calling from Florida.

“My mom just called me and said that Colt texted his mom – my sister – and his dad that he was sorry, and they called the school and told the counselor to go get him immediately,” the woman said through tears. “She said she saw that there’s been a shooting, and I’m just worried it was him.”

According to an earlier report from The Washington Post, the teen's mother told her sister that she called the school half an hour before the shooting began and said there was an "extreme emergency" with her son.

Gray is being charged with murder for the deaths of students Mason Schermerhorn and Christian Angulo, both 14, and teachers Ricky Aspinwall, 39, and Cristina Irimie, 53. Eight other students and one teacher were injured. Gray's father, Colin Gray, also faces charges of involuntary manslaughter, second-degree murder and cruelty to children.

The release of the 911 calls comes amid ongoing services for some of the victims planned for Saturday.

A memorial service for Mason Schermerhorn, a ninth grader who "loved Disney World and LEGOs," was scheduled for Saturday afternoon at a civic center and attendees were asked to wear his favorite color, red. Cristina Irimie, a math teacher and pillar of her tight-knit Romanian Orthodox community, is set to be remembered at a separate service in the afternoon.