About 20 firefighters were on scene at Dubbo South Public School after a blaze broke out on Thursday afternoon.
All students have been evacuated and accounted for, after the blaze broke out around 2.30pm.
Fire and Rescue NSW (FRNSW) spokesperson has reported four classrooms are completely engulfed in flames, while they battle to protect another.
Three firefighters are believed to have reported to NSW Ambulance paramedics for health checks.
Three FRNSW crews, one Rural Fire Service crew, Ambulance and police are at the scene. Firefighters have put protections place to ensure the fire doesn't spread to nearby buildings.
One bystander, who arrived shortly after the fire broke out, said the scene was distressing, with both parents and young students visibly distraught.
"It was pretty scary," she said.
"You could just see a massive, it almost look like a tornado of flames it was so high up, and the smoke was billowing out.
Then all you could see was just parents coming from every which direction, they had the kids all lined up, so they couldn't see [the fire]."
She praised the staff who were calm and composed throughout.
The cause of the blaze is yet to be determined.
FRNSW Superintendent Scott Dodson said this was a timely reminder that calling Triple Zero (000) for a fire emergency could be the difference between life and death, or a building or other property being saved.
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