At just after 6 p.m. on Saturday, fire crews from Hampshire and the Isle of Wight were called to the former Brune Park School on Military Road in Gosport.
Firefighters are expected to work through the night to put out a fire at a former secondary school in Gosport.
There were no injuries. The cause of the fire is unknown, but a joint police and fire investigation has been launched.
At the height of the blaze, six fire engines were on the scene.
Police were on the scene to assist the fire service and manage the nearby road closures.
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