Emergency services were called to the scene at about 3.40pm, where they found the building in the construction area well-alight with black smoke billowing into the sky.

Onlookers had ash rain upon them as the firies worked on the blaze, and police blocked off Little Bloomfield Street and Henry Street.

They gained control of the fire just past 5pm.

A Fire and Rescue NSW spokesperson said all students and workers were accounted for, and that the blaze began in the roof of the building.

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Police, NSW Ambulance, three Fire and Rescue NSW crews and two Gunnedah RFS crews are all on the scene.

It is unknown at this stage how the fire started.

More to come soon.