"When we arrived on the scene, the roof was fully engulfed," said Debbie Tanna, Cumberland County Sheriff's Office spokesperson.
The blaze was too big to battle from inside the building.
"We don't want to hurt anybody on a fire like this, so we decided right away to stay on the outside and do what we can from the outside," Battalion Commander Scott Iverson said.
Firefighters said the brick walls helped keep flames from spreading to the rest of the school. However, after the fire was under control, crews did not risk going inside.
"The roof has fell into that area, and it's covering everything so we're not sure what's inside," Iverson said.
Investigators have not determined a cause, and no injuries were reported.
"What caused that fire -- we don't know right now," Tanna said. "We're not ruling out anything, but it does not appear to be arson at this time."
The school gym was destroyed, which means a lot of work will need to be completesd by the time students return to school on August 25.
"It'll certainly be a challenge, but we'll have to make it happen," said Wanda McPhaul, Cumberland County Schools.
There is speculation that lightening or fireworks may have sparked the fire, but investigators will not be able to confirm the cause until they are able to get inside the building.
Once the building is inspected, school leaders will have a better idea of what they need to do in order to be ready for the start of school.
The sheriff's office, the SBI and the Fayetteville Police Department is participating in the investigation.