Crews used 10 breathing apparatus, two hose reels, two jets, two compressed air foam jets and the aerial ladder platform to bring the fire at Winton School in Andover under control.
Group Manager Dan Tasker said: "The first crews to arrive were met with a challenging situation of a confirmed fire plus the evacuation of 500 pupils."
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Police have confirmed a body of a woman has been found by officers searching for Gaia Pope.